Method and device for stripping ammonia from liquids

ABSTRACT

The present invention provides a method and a system for stripping volatile compounds such as ammonia from liquids. Part of the ammonia is stripped from the liquid in a system having a shunt through which liquid such as e.g. fermented biomass can be diverted in the form of a side stream in liquid contact with a main fermentor(s). The stripper system is connected to an evaporator. In the evaporator aqueous liquid is heated at a pressure below atmospheric pressure whereby vapor is developed at a temperature below 100° C. The vapor from the evaporator is directed to the liquid medium containing ammonia and this results in ammonia being stripped from the liquid and transferred to the vapor phase. The vapor phase is condensed in a first condenser at a low pressure, and the liquid thus obtained is further treated in a stripper unit at a higher pressure.

FIELD OF THE INVENTION

The present invention relates to a method for stripping off ammonia fromliquids by contacting said liquids with vapour at low pressure or undervacuum, a system comprising a shunt and a stripper device in which theammonia is stripped from the liquid medium comprising ammonia, a mobileunit comprising such a system, and a plant wherein a liquid mediumcomprising ammonia is generated during e.g. fermentation, wherein saidplant comprises said system for stripping ammonia from the liquid.Ammonia comprising liquids generated during operation of e.g. biogasplants can be handled by the system.

BACKGROUND OF THE INVENTION

Industrial plants for production of sugars, alcohols, industrialenzymes, medicaments and the like as well as different energy plants forproduction of renewable energy from biomass is usually based on theactivity of microorganisms under either aerobic or anaerobic conditionsin process tanks. Examples are the production of insulin and beveragesby yeast under anaerobic conditions in fermentation tanks where thesubstrate is malt or molasses, or a similar agricultural plant productrich in carbohydrates.

The treatment of waste is another area widely accepted as a proventechnology and extensively used. Also in this case microorganisms inaerobic/anaerobic process tanks digest the waste. However, not onlymunicipal sewage waste but also a number of various industrial andagricultural wastes are also treated through microbiological means.

The microbial activity is based on the growth kinetics of the differentgroups of microorganisms involved and of the activity of a number ofspecific enzymes necessary to perform the biochemical processes. Theoverall result of the processes is microbial growth, substrateconsumption, and product formation. However, enzymes and microorganismsmay be inhibited by the main products or side products, which accumulatein the process tank or any other substance resulting from the microbialtransformations of the substrate. Also substances in the biomass or thesubstrate in it self may hamper optimal performance of the bioreactor.Such inhibition may lead to a substantially lower microbial activity andthus substantially lower production and perhaps a complete break down ofthe microbial process if the inhibitory substances are not carefullycontrolled.

Such risks are usually avoided or controlled by managing the substrateloading or the organic loading rate, the rate being set to ensure aconcentration of the critical component below levels unacceptable to theprocess. Other process parameters such as temperature, pH, salinity,media composition, and the microbial consortia employed may also beselected according to the process optima. However, managing the organicloading rate at low inputs to the bioreactors inevitably result in lowproduct formation and a poor performance of the process in general. Thecontrol of the other process parameters such as temperature and pHcompensates only partly for the inhibition by the inhibitory substanceor substances. A direct control of the inhibitory substance at levelssub critical to the process is far the most effective control ifpossible.

It is often desirable to remove volatile components from microbialprocess tanks during continued operation of the process, i.e. theinhibitory substance is continuously removed yet the process and themicroorganisms are left unaffected.

Generally, volatile components can be separated from a liquid by airstripping or vapor stripping, such as e.g. steam stripping of ammoniafrom aqueous solutions, or e.g. steam stripping of methanol.

Methods and systems for vapor stripping of volatile components fromliquids comprise steps and means for producing a vapor of volatilecomponents, such as ammonia, from the liquid. Typically, evaporationmeans requires energy from a suitable heating medium, typically aheating medium of high value such as e.g. electricity or combustionfuel, whereas available on-site heating media often are low-valuedheating media such as cooling media comprising otherwise wasted heatfrom e.g. combustion of organic waste gases in an engine.

For effective removal of volatile components from liquids at atmosphericpressure, large amounts of steam or heat are required. Consequently,typical vapor stripping apparatus comprises large, energy consuming, andexpensive components, which are not suited for small in-situ liquidtreatment systems, such as system for treatment of liquids of manure atanimal farming sites.

U.S. Pat. Nos. 5,385,646, 5,498,317, 5,643,420 and 5,779,861 disclose anapparatus and method for treating process condensate from a chemicalproduction plant wherein contaminants are substantially removed from acondensate by steam stripping and subsequent rectification in arelatively low pressure stripping/-rectification tower. A portion ofcondensed overhead and scrubbing aqueous liquid-containing contaminantsis returned to the top of the rectification section of the tower asreflux and the balance is withdrawn as a concentrated steam.

DE 43 24 410 C1 discloses a method of removing ammonia from wasteaqueous liquid of a biological waste treatment plant, the methodconsisting of a two step process: a first step comprising strippingammonia from the waste aqueous liquid by steam at atmospheric pressure,condensing said steam comprising stripped ammonia, and producingcondensation heat for producing said steam; and a second step comprisingrectifying said condensed steam comprising ammonia to at least 20% byweight of aqueous ammonia, said second step advantageously being carriedout at a pressure above atmospheric pressure.

SUMMARY OF THE INVENTION

There is a need for an improved method and an apparatus for separationof volatile components from a liquid, which method and apparatus issimple and economic in operation allowing low-valued heating media to beused, and which method and apparatus avoid large, energy consuming, andexpensive components.

The present invention aims to remove undesirable or inhibitory volatilecomponents from microbial process tanks during continued operation ofthe process. The inhibitory substance is continuously removed and theprocess and the microorganisms are left unaffected.

Although anaerobic digestion of agricultural waste such as animalmanures is well established, the digestion of swine slurry is difficultdue to a high content of ammonia in the manure and a relatively smallcontent of solids. The solids consist of complex carbohydrates mainlyincluding small amounts of proteins and fats.

The inhibition by ammonia is substantial at contents of more thanapproximately 1 kg free ammonia-N per tonnes swine slurry, where freeammonia-N is NH₃ (s) and not the dissolved ammonia ion NH₄ ⁺ (s). Theconcentration of gaseous ammonia NH₃ (g) is under normal circumstancesmuch lower than the NH₃ (s) concentration. The concentration of freeammonia is a function of temperature and pH. For example, at a totalN-content of 6 kg per tonnes swine slurry the concentration of freeammonia at pH 8 is about 0.75 kg/tons at 37° C., 1.4 kg/tons at 45° C.,1.6 kg/tons at 55° C., and 2.6 kg/tons at 60° C. (e.g. Hansen K. V., 1.Angelidaki, B. K. Ahring (1998) Anaerobic digestion of swine manure:Inhibition by ammonia. Aqueous liquid Research 32. 5-12).

The swine slurry is therefore in conventional systems often mixed withcattle slurry or other biomasses rich in carbohydrates to achieve abiomass mixture, which is easier to digest. The operating temperature isalso often set at mesophile temperatures about 45° C. or lower, wherethe free ammonia content is relatively small. However, the efficiency ofsuch schemes is relatively low.

A far higher efficiency would be achieved if the ammonia content wasmonitored and controlled by continuously removing ammonia above acertain threshold value. This would enable the process to be run atthermophilic temperatures around 60° C. where the microbial activity ismuch higher.

As a rule of thump the microbial activity doubles for each 10s increaseof temperature. If ammonia could be controlled, it would be preferableto operate biogas plants at about 60° C. (e.g. Ahring B. K., A. A.Ibrahim, Z. Mladenovska (2001) Effect of temperature increases from 55to 65° C. on performance and microbial population dynamics of ananaerobic reactor treating cattle manure. Aqueous liquid Research 35.2446-2452).

Several biogas plants co-digest animal manures and industrial waste orother biomasses in order to achieve a biogas production, which renderthe enterprise economical in terms of reasonable pay back times andrevenue. It is in general not possible to arrive at a sound economy forplants digesting animal manures only and addition of supplementarybiomasses are therefore necessary. However, several biomasses ofagricultural origin contain large amounts of proteins or ammonia andthese substrates are therefore difficult to co-digest with animalmanures in any significant quantities. Such biomasses include animalbi-products, such as meat and bone meal, vegetable proteins, as well asmolasses and vinasse and similar products.

One particularly interesting animal bi-product is meat and bone meal.Meat and bone meal contains between 55-60% protein, 7-14% lipids, and2-5% aqueous liquid so approximately 9% of the meat and bone meal isnitrogen. One tonnes of meat and bone meal thus contains approximately90 kg N.

A typical N-content in animal manure is about 6 kg N per tonnes slurryand the critical content is 4-6 kg N per tonnes. Higher amountsinevitably leads to break-down of the process, which is already hamperedat the 6 kg N per tonnes. Addition of e.g. 5% meat and bone meal wouldadd 4.5 kg N per tonnes slurry and it has so far been possible to addonly very small percentages of about 2.5% of meat and bone meal toanimal slurries, which are to be digested in biogas plants. However, bycontinuously removing the liberated ammonia as disclosed by the presentinvention it is possible to add e.g. a 10-fold amount of 25% meat andbone meal and thus benefit from the biogas potential of the meat andbone meal, while concentrating the ammonia in a separate fraction wellsuited as fertilizer.

Even though the ammonia content of a particular substrate can also beremoved before degassing in the biogas reactor, substrates with highprotein contents release their nitrogen content as ammonia within thebioreactor during the digestion and thus during the methane formationfrom the substrate. A pre bioreactor removal of ammonia from the Ncomprising substrates including proteins is therefore not alwayssufficient. However, the present invention allows a continuous removalof ammonia generated during fermentation within the bioreactor. Anycontent of ammonia already present in the influent may also be removedby the method and system of the invention. The present invention in afirst aspect provides a method and a system for stripping ammonia fromliquid medium comprising ammonia or precursors thereof, such as e.g.liquids in biogas reactors. Part of the ammonia is stripped from theliquid in a stripper system comprising a shunt through which liquid suchas e.g. fermentation medium comprising a biomass can be diverted in theform of a side stream in liquid contact with a main fermentor(s). Thestripper system is connected to an evaporator. In the evaporator aqueousliquid is heated at a pressure below atmospheric pressure whereby vaporis developed at a temperature below 100° C.

The vapor from the evaporator is directed to the liquid mediumcomprising ammonia and this results in ammonia being stripped from theliquid and transferred to the vapor phase. The vapor phase is condensedin a first condenser at a low pressure, e.g. a pressure below 1 bar,such as a pressure of less than 0.5 bar, and the liquid thus obtainedcan be further treated in a stripper unit at a high pressure, such ase.g. a pressure at or above 1 bar, but preferably below 5 bar, saidtreatment resulting in the generation of a more concentrated ammoniacomprising fluid or liquid. When stripped for at least a substantialpart of the ammonia the liquid initially obtained from the biogasreactor and diverted to the shunt can be returned to the reactor.

Definitions

Cold steam means steam at a temperature below 100° C. and at a pressurebelow 1 bar. As an example, cold steam can be generated by e.g. heatingaqueous liquid to about 50-80° C. and lowering the pressure above theaqueous liquid surface to 0.1 to 0.3 bar, whereby a steam is obtained.

Hot steam means steam generated at a pressure of 1 bar or more.

NH₃ (g) means NH₃ in gaseous phase

NH₃ (s) means NH₃ in soluble (liquid) phase

NH₄ ⁺ (s) means NH₄ ⁺ in soluble (liquid) phase

Vapor stripping means stripping of volatile compounds from a media bydirecting vapor through the medium.

Shunt is a device to which fermentation/reactor liquids can be shuntedand wherein volatile compounds comprised in said liquids can be strippedoff by using cold steam, i.e. steam at a temperature below 100° C. andat pressure below a predetermined reference pressure such as e.g. 1 bar.

Stripper unit is a device wherein volatile compounds can be stripped offa liquid at a pressure at or above a predetermined reference pressuresuch as e.g. 1 bar.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the stripper device and the main process stepsaccording to one preferred embodiment of the invention. The figureillustrates a biogas reactor (R), a shunt (S), an evaporator (E), astripper unit (K3), a first condensing device (K1), a further optionalcondensing device (K2), and a second condensing device (K4). When K2 isnot present, first condensed liquid medium is diverted directly to thestripper unit (K3).

FIG. 2 illustrates another embodiment of the stripper device of theinvention. In this embodiment, the invention is capable of beingexploited as a mobile unit.

FIG. 3 illustrates one preferred embodiment of the shunt, the stripperunit and associated condensing device(s) of the present invention.

FIG. 4 illustrates possible ways of integrating the shunt, the stripperunit and associated condensing device(s) of the present invention withone or more fermentors or biogas reactor(s) forming part of a plant forprocessing organic material.

FIGS. 5 and 6 in combination illustrate the units of another plant forprocessing organic material. Also in this case is it possible tointegrate the shunt, the stripper unit and associated condensingdevice(s) of the present invention with one or more fermentors or biogasreactor(s) forming part of a plant for processing organic material.

FIG. 7 is an illustration of a flow diagram depicting a simplificationof the shunt and the connected processing plant according to theinvention and processes relating thereto.

DETAILED DESCRIPTION OF THE INVENTION

The below sections disclose in more detail preferred embodiments of thepresent invention relating to a system comprising a shunt and stripperdevice(s) for stripping volatile compounds such as e.g. ammonia from aliquid comprising such volatile compounds. The system and/or the methodsof the present invention can be used to:

eliminate or reduce the emission to the environment of dust, microbialorganisms, ammonia, contaminated air, liquid or any other constitutionwithin the system, especially from animal houses. This would requireintegration of the invention with a system comprising animal houses,biogas and nutrient refinement.

improve the utilisation of the energy contained in a biomass includingorganic material.

improve the production of biogas comprising methane gas andmethane-bearing gas. Said gas may be stored in a tank locally and/or canbe diverted to a commercial net of distributing gas and/or beincinerated in a gas motorgenerator to produce electricity and heat.

obtain separate fractions of N (nitrogen), P (phosphor) and potentiallyK (potassium) from organic materials. Said fractions are of commercialvalue and can be utilised as fertilisers to fertilise agricultural andhorticultural crops. The separate fractions of P and K can be isolatedfrom the remains from the organic materials subjected to anaerobicfermentation. The remains in the form of a slurry comprising solids andliquids are preferably diverted to at least decanter centrifuge forseparating solids and fluids. One result of this separation is an atleast semi-solid fraction preferably comprising almost exclusively P(phosphor), or an at least semi-solid fraction preferably comprisingfrom 2 to 10% (w/w) P. In the same step, or in another decantercentrifuge separation step, a liquid fraction preferably comprisingalmost exclusively K (potassium), or a liquid fraction preferablycomprising about 5 to 15% (w/w) K can preferably also be obtained. Thesefractions, preferably in the form of granulates obtained after a dryingstep, including a spray drying step or a slurry drying step, comprise Pand/or K in commercially acceptable purities readily usable forcommercial fertilisers. Such fertilisers may be spread onto crops oragricultural fields. The liquids resulting from decanter centrifugeseparation step(s), such as reject water, can also be diverted toagricultural fields, they can be diverted back to e.g. a stable oranimal house, or into a sewage treatment system.

obtain an improved animal welfare and improved hygiene in animal stablesand in accordance to output from said animal stables. Said outputcomprising manure, slurry and animals to be slaughtered. The cleananimals reduces the risk of infection of meat when the animals areslaughtered. The processing of the animal waste by means of theinvention in biogas and nutrient refinement plants also reduces the riskof spreading viral and microbial organisms and pathogens to theenvironment.

obtain a procedure for rendering animal carcases or fractions hereof,meat and bone meal or any other produce from animals available fordisposing off to agricultural land in the form of refined fertilizersand thus to benefit from micro- and macro-nutrients in the animalproduce in the agricultural or horticultural plant production.

Working Principle of the Invention

Anaerobic microorganisms are obligate anaerobic and conventional ammoniastripping systems using e.g. atmospheric air is therefore not possible.Stripping with inert gasses is not very efficient or economicallyfeasible. Likewise, it is not acceptable to apply conventional steamstripping because the temperature would kill off the important microbialorganisms. The solution provided by the invention is therefore based oncold steam and vacuum because the microorganisms are tolerant to evenvery low pressures.

One step of the process step of the invention involves a firstcondensing device (K1). This step generates a first condensed aqueousliquid and a vapor not condensed by the first condensing device. Thefirst condensing device operates at a low pressure below saidpredetermined reference pressure, preferably a reference pressure of 1bar. Vapor not condensed by the first condensing device is optionallydiverted in a further process step to a further condensing device (K2)at a pressure below the predetermined reference pressure. The objectiveis to remove a substantial part of the remaining volatile compounds suchas e.g. ammonia from said vapor not condensed by the first condensingdevice. The objective is achieved by including a washing step using acounter current of aqueous liquid, obtaining an aqueous liquid fractioncomprising volatile compounds such as e.g. ammonia and optionally vapornot condensed by the further condensing device.

A further process step comprises diverting said first condensed aqueousliquid from K1, and optionally also said aqueous liquid fraction fromK2, comprising volatile compounds such as e.g. ammonia from the firstcondensing device, and optionally also from the further condensingdevice, respectively, to said stripper unit (K3), where saidcondensate(s) are stripped of the volatile compounds such as e.g.ammonia by heating at a second pressure which is higher than the firstpressure, preferably a pressure of 1 bar or more, and obtaining a hotvolatile compound such as e.g. ammonia-comprising steam and aqueousliquid stripped off a substantial part of the volatile compounds such ase.g. ammonia.

The higher second pressure is obtained by heating the liquid mediumcomprising the aqueous liquid fraction from K2 comprising volatilecompounds such as e.g. ammonia and/or the first condensed aqueous liquidmedium from K1 comprising volatile compounds such as e.g. ammonia in thestripper unit K3 to a temperature of more than 100° C., such as morethan 105° C., for example more than 110° C., such as more than 115° C.,for example more than 120° C., such as more than 125° C., for examplemore than 130° C., such as more than 135° C., for example more than 140°C., such as more than 145° C., for example more than 150° C., such asmore than 155° C., for example more than 160° C., such as more than 165°C., for example more than 170° C., such as more than 175° C., forexample more than 180° C., such as more than 190° C., for example morethan 200° C., and preferably less than 250° C.

In a preferred embodiment, a volume of bioreactor liquid comprisingactive biomass from the bioreactor is pumped to the shunt (S) asmentioned herein above, where cold steam at a temperature of from about50° C. to about 65° C., such as from about 55° C. to about 65° C., forexample from about 60° C. to about 65° C., such as from about 50° C. toabout 60° C., for example from about 50° C. to about 55° C., such asfrom about 55° C. to about 60° C., for example from about 57° C. toabout 62° C., such as about 60° C., is diverted to the shunt held undera vacuum of from about 0.05 to about 0.4 bar, for example from about 0.1bar to about 0.4 bar, such as from about 0.15 bar to about 0.4 bar, forexample from about 0.2 bar to about 0.4 bar, such as from about 0.25 barto about 0.4 bar, for example from about 0.30 bar to about 0.4 bar, suchas from about 0.35 bar to about 0.4 bar, for example from about 0.05 barto about 0.35 bar, such as from about 0.05 bar to about 0.3 bar, forexample from about 0.05 bar to about 0.25 bar, such as from about 0.05bar to about 0.2 bar, for example from about 0.05 bar to about 0.15 bar,such as from about 0.05 bar to about 0.1 bar, for example from about 0.1bar to about 0.15 bar, such as from about 0.15 bar to about 0.2 bar, forexample from about 0.2 bar to about 0.25 bar, such as from about 0.25bar to about 0.3 bar, for example from about 0.3 bar to about 0.35 bar,such as from about 0.35 bar to about 0.4 bar, depending on the runningtemperature of the bioreactor.

The cold steam obtained in the evaporator (E) is directed through theliquid medium comprising the active biomass in the shunt (S), which isequiped with diffusers. While contacting the reactor liquid comprising abiomass, the steam strips off volatile compounds such as e.g. ammonia.

The generated vapor/steam comprising volatile compounds such as e.g.ammonia preferably comprises about 1-10% volatile compounds such as e.g.ammonia, such as 2-10% volatile compounds such as e.g. ammonia, forexample 3-10% volatile compounds such as e.g. ammonia, such as 4-10%volatile compounds such as e.g. ammonia, for example 5-10% volatilecompounds such as e.g. ammonia, such as 5-9% volatile compounds such ase.g. ammonia, for example 5-8% volatile compounds such as e.g. ammonia,such as 5-7% volatile compounds such as e.g. ammonia, such as 6-10%volatile compounds such as e.g. ammonia, for example 7-10% volatilecompounds such as e.g. ammonia, such as 8-10% volatile compounds such ase.g. ammonia, for example 9-10% volatile compounds such as e.g. ammonia,such as 1-9% volatile compounds such as e.g. ammonia, for example 1-8%volatile compounds such as e.g. ammonia, such as 1-7% volatile compoundssuch as e.g. ammonia, for example 1-6% volatile compounds such as e.g.ammonia, such as 1-5% volatile compounds such as e.g. ammonia, forexample 1-4% volatile compounds such as e.g. ammonia, such as 1-3%volatile compounds such as e.g. ammonia, for example 1-2% volatilecompounds such as e.g. ammonia, such as 2-4% volatile compounds such ase.g. ammonia, for example 4-6% volatile compounds such as e.g. ammonia,such as 6-8% volatile compounds such as e.g. ammonia, for example 8-10%volatile compounds such as e.g. ammonia, such as 2-3% volatile compoundssuch as e.g. ammonia, for example 3-4% volatile compounds such as e.g.ammonia, such as 4-5% volatile compounds such as e.g. ammonia, forexample 5-6% volatile compounds such as e.g. ammonia, such as 6-7%volatile compounds such as e.g. ammonia, for example 7-8% volatilecompounds such as e.g. ammonia, such as 8-9% volatile compounds such ase.g. ammonia, and this steam is subsequently condensed at a low, firstpressure (in K1) and further concentrated (stripped) at higher secondpressure (in K3) to achieve preferably a solution of as much as 25%volatile compounds such as e.g. ammonia in aqueous liquid, such as forexample 22% volatile compounds such as e.g. ammonia in aqueous liquid,for example 20% volatile compounds such as e.g. ammonia in aqueousliquid, for example 18% volatile compounds such as e.g. ammonia inaqueous liquid, for example 16% volatile compounds such as e.g. ammoniain aqueous liquid, for example 14% volatile compounds such as e.g.ammonia in aqueous liquid, for example 12% volatile compounds such ase.g. ammonia in aqueous liquid, for example 10% volatile compounds suchas e.g. ammonia in aqueous liquid, for example 8% volatile compoundssuch as e.g. ammonia in aqueous liquid, and preferably a solution ofmore than 5% volatile compounds such as e.g. ammonia in aqueous liquid.

The target concentration of e.g. ammonia in the biogas reactor is about3 kg N per tonnes, or less, such as about 2.9 kg N per tonnes, forexample 2.8 kg N per tonnes, such as about 2.7 kg N per tonnes, forexample 2.6 kg N per tonnes such as about 2.5 kg N per tonnes, forexample 2.4 kg N per tonnes such as about 2.3 kg N per tonnes, forexample 2.2 kg N per tonnes, such as about 2.1 kg N per tonnes, forexample 2.0 kg N per tonnes, such as about 1.9 kg N per tonnes, forexample 1.8 kg N per tonnes, such as about 1.7 kg N per tonnes, forexample 1.6 kg N per tonnes, such as about 1.5 kg N per tonnes.

This target concentration is set based on two considerations. Firstly,the ammonia inhibition is released even at running temperatures of 60°C. in the bioreactor. Secondly, it is energetically easier to strip the“upper” N from 3 kg to e.g. 1.5 kg N than a complete stripping toperhaps 10 ppm ammonia. This also leaves some N remaining in thebioreactor for the metabolism of the microorganisms.

Advantages Associated with the Invention

Using this invention a number of advantages are achieved:

1. The ammonia concentration of active bioreactors is controlled and theco-digestion of N-rich wastes such as N-containing animal bi-products,including meat and bone meal, with animal manures is rendered possible.

2. Ammonia is removed from the biomass and a pure N-fertiliser ofcommercial value is produced.

3. It has surprisingly turned out that by providing a two-step strippingprocess a relatively low amount of energy (steam) is necessary. Asexplained in detail herein above, a heating media of low value, such aswaste heat, can be used to provide the cold steam. The first strippingstep comprises stripping volatile compounds such as e.g. ammonia fromthe active biomass at reduced pressure (preferably e.g. 0.1 to 0.2 bar)below a predetermined reference pressure (preferably e.g. 1.0 to 2.5bar, more preferably 1.0 bar), where the steam/volatile compounds suchas e.g. ammonia steam (typically comprising about 4-6% ammonia) cansubsequently be condensed at the said low pressure in a first condensingdevice (K1), and optionally also in a second condencing device (K2)condensing cold volative compound or ammonia steam not condensed in thefirst condensing device.

The second stripping step comprises stripping volatile compounds such ase.g. ammonia from said condensed liquid obtained from the firststripping step. The second stripping step is carried out by injectinghot aqueous steam into the stripper unit (K3), thereby generating apressure at or above the pre-determined reference pressure in thestripper unit. The stripping ultimately results in condensing the hotsteam comprising volatile compounds such as e.g. ammonia, therebygenerating a condensate comprising as much as about 25% volatilecompounds such as e.g. ammonia in an aqueous liquid solution.

The condensate obtained from the first stripping step (i.e. condensateobtained in K2) can preferably be diverted to a storage tank in whichthe pH of the condensate can be adjusted before the condensate isstripped for ammonia in the second stripping step. After pH adjustmentthe pH value of the condensate is preferably 9 or more, such as 9.5, forexample 10.

4. The disclosed system also makes it possible to control thetemperature in the biogas reactors. If the vacuum of the shunt is setsomewhat lower than the vapor pressure of the active biomass, a netevaporation from the biomass will occur thus lowering the temperature ofthe active biomass (to be returned to the bioreactor). On the otherhand, if the vacuum of the shunt is set somewhat higher than the vaporpressure of active biomass a net condensation will occur thus increasingthe temperature of the biomass (to be returned to the bioreactor).

5. Low pressure (and thus cold steam as defined herein) provides thehighest stripping efficiency per kg steam.

6. The invention provides an efficient and economical heat exchangerbetween warm wastewater or aqueous liquid and very inhomogeneous slurryor biomass. It is thus possible to replace mechanical plate heatexchangers, which are costly and difficult to manage due to scaling andfouling of heat exchange plates. Scaling results from precipitation ofe.g. calcium carbonates or struvite, while fouling is often caused byadsorption of proteins to the plates.

If the process involves a heat exchanger between slurry in a slurry tankand wastewater or aqueous liquid, the pressure in the slurry tank ispreferably higher than the vapor pressure of the slurry, but lower thanthe steam vapor in the steam generator. In this case the generated coldsteam will effectively condensate in the slurry and thus release theheat to the slurry.

The wastewater or aqueous liquid for cold steam production can beuntreated aqueous liquid comprising e.g. salts, suspended solids, drymatter etc. It is not necessary to clean the wastewater or aqueousliquid before steam production from the waste. The generated cold steamfrom e.g. such wastewater is directed through the liquid mediumcomprising volatile compounds such as e.g. ammonia within the shunt ofthe stripper device. The cold steam produced in e.g. an evaporatorenters the shunt of the stripper device by diffusers located inside theshunt.

The heat exchangers of the system described herein above are cheap tomanufacture and operate.

System Comprising a Stripper Device for Stripping Volatile Compounds

In a first preferred aspect of the invention there is provided astripper device comprising a shunt and applications thereof forstripping ammonia as described herein.

A side stream is diverted from an active bioreactor to the shunt where asubstantial part of the ammonia content is removed before the sidestream is diverted back to the bioreactor. This is illustrated inFIG. 1. The ammonia is removed to an extent, which allows the bioreactorto operate efficiently.

A second principal application is where the stripper device according tothe present invention is used for an end-stripping purpose (such as e.g.illustrated in FIG. 6, component 2, “stripper 2”). In this application,a liquid such as e.g. reject water resulting from decantercentrifugation is purified from ammonia, i.e., it is stripped to verylow concentrations of less than e.g. 200 ppm, such as less than 100 ppm,for example less than 50 ppm or even 10 ppm before the liquid is reusedor disposed. In this case the liquid is preferably not shunted back to abioreactor or any other process tank, but is simply purified to anextent, which allows reuse or final disposal of the liquid.

In the latter case a modified stripper unit is used where cold steampasses a column with course packed filter material over which the liquidis allowed to percolate in a counter current against the steam. This isnecessary to achieve the stripping efficiency required to reach the lowlevels of ammonia, i.e., less than e.g. 50 ppm.

As an alternative to a column with course packed filter material one canapply a fluid bed column. One example of such a column is disclosed inU.S. Pat. No. 5,588,986 incorporated herein by reference.

Typically the stripping devide comprises a stripping column thecharacteristics of which has been designed according to methods known inthe art, including but not limited to designs based on the commercialsoftware design package Hyses™. Typically, it is preferred to use thestripping columns having 8-12 theoretical plates. A practicalconstruction of such a stripping column, including design of columnplates, inter-plate conduits, selection of column package materialsetc., is known to a person skilled in the art. Commercial strippingcolumns are generally available from chemical engineering suppliers. Theremaining components of the end-stripper application system are similarto the shunt application.

The stripper device K3 can be constructed to simulate a conventionalstripper column where the stripping is performed by means of a countercurrent of steam against a current of percolation liquid.

However, it shall be designed to allow stripping of ammonia from a thickor viscous liquid with a high dry matter content of 10-50% typicallybetween 10-20%, i.e. a typical liquid from an active bioreactor.

The column is prepared not by packing by filter material but isconstructed with a number of horizontal plates with small holes and anopening for downward movement of the liquid from one plate to thefollowing plate. The plates are placed at regular distances throughoutthe column.

The holes in the plates shall allow the cold steam to pass through theplates and the thick liquid thus striping off the ammonia. At the sametime the steam shall keep the liquid and the dry matter in suspension soas to prevent settling of material on the plates.

The number of holes, plates and the amount of steam shall be adjusted toachieve the high stripping efficiency.

In a further aspect there is provided a system for reducing theconcentration of volatile compounds in a liquid. Examples of volatilecompounds include any compound capable of being stripped off a liquidmedia by vapor stripping/heating, optionally vapor stripping/heatingunder reduced pressure (i.e. below 1 bar), and subsequently collected bycondensation of the vapor/steam generated as a result of thestripping/heating process. One example of a volatile compound isammonia. Another example of volatile compounds is amines. Systemsaccording to the invention can be designed for stripping off one or morevolatile compounds present in a liquid medium. In one preferredembodiment the system is designed for stripping off ammonia from anaqueous liquid.

The systems according to the invention comprise technical featuresnecessary for carrying out the methods of the invention as disclosedherein.

In one embodiment there is provided a system comprising a stripperdevice, said stripper device comprising

a) a shunt (S) for stripping off volatile compounds from a liquidmedium, wherein the shunted liquid medium is in liquid contact with aprocessing plant such as e.g. fermentor or a biogas reactor,

b) a heat source, e.g. warm aqueous liquid, diverted to an evaporator(E), for producing cold steam to be diverted to the shunt (S),

c) at least one condensing device (K1 and optionally K2) forcondensing—preferably at a pressure below 1 bar—volatile compoundsstripped off the liquid medium comprised in the shunt (S),

d) a stripper unit (K3) for stripping by injection of hotsteam—preferably stripping at a pressure at or above 1 bar—volatilecompounds from a condensate generated by said at least one condensingdevice, and

e) optionally a second condensing device (K4) for condensing volatilecompounds stripped from the stripper unit, and

f) valves, pipes and, when required, pumps for connecting the shunt tothe heating source, to the condensing device(s) and to the stripperunit.

The condensates obtained with the present invention are obtained as aresult of cooling of vapor/steam and not by compression.

The shunt preferably comprises an entry compartment in the form of apre-degassing unit capable of regulating the composition of the coldsteam being diverted to the condensing device(s). The bio-mass entersthe pre-degassing unit via a plurality of spray nozzles capable ofdistributing the bio-mass to the surfaces of the splash plates.

It is preferred that primarily ammonia is diverted to the condensingdevice(s). Accordingly, the degassing unit preferably diverts gassessuch as methane, carbondioxide and hydrogendisulphide to an air scrubberwhile ammonia is diverted from the pre-degassing unit to the shunt.Methane comprising gas can subsequently be diverted to a gasmotor inorder to produce electricity and heating.

The pressure in the degassing unit depends on the temperature of theorganic material being diverted to the pre-degassing unit. For a giventemperature, the pressure in the pre-degassing unit will be higher thanthe pressure at which water boils at the temperature selected. Typicallythe pressure will be in the range of from 0.15 to 0.30 bar. Thetemperature in the pre-degassing unit will be above the boiling point ofsaturated aqueous vapor at the pressure in question.

The reason for the selection of a pressure higher than the pressure atwhich water boils at a given temperature is in order to prevent waterand ammonia from evaporating in the pre-degassing unit. Also, thepressure must be sufficiently high so as to retain bicarbonate in theliquid phase. The retention of bicarbonate reduces the amount ofcarbondioxide produced.

The pressure in the pre-degassing unit is preferably provided by aliquid ring pump or a capsule blower. The pre-degassing unit preferablycomprises splash plates to ensure a sufficient exposure of the liquidsso that the gasses can be generated.

The volume of the pre-degassing unit shall be sufficient to ensure thatthe gasses can be generated and extracted within a suitable time,preferably less than about 10 seconds.

From the pre-degassing unit, the liquid bio-mass enters the shunt bymeans of a disc flow pump or an eccentric pump. Alternatively, vacuumcan be used for transferring the liquid bio-mass from the pre-degassingunit and into the shunt compartment.

The cold steam from the evaporator can be diverted directly to the shuntor to the biomass entering the shunt.

One example of flow conditions and cold steam injection is:

Input parameters: Biomass flow 60 m³ per hour Temperature 55° C. Ammoniacontent 3 kg per m³ Steam flow 5.000 m³ per hour(in one example 4.000 m³ per hour from cold steam addition to the shunt,1.000 m³ per hour from cold steam being used for cooling the biomass)Output Parameter:

Ammonia removal, up to 75 kg/hour,

Production of steam comprising an ammonia concentration of from 0,5 toabout 5% ammonia.

Parameters for Stripper Unit (K3):

Steam flow 300 kg/hour at 2,5 bar at a temperature above 100° C. (e.g.140° C.).

Output Parameter:

75 kg ammonia/hour as a condensate of up to approx. 25% ammonia.

The system according to the invention comprising the stripper device canfurther comprise a fermentor or a biogas reactor in liquid contact withthe shunt as well as a container for collecting the stripped off andcondensed volatile compounds.

Additionally, the system can comprise a pre-treatment plant. Substratesare processed in the pre-treatment plant prior to entering e.g. thefermentor or the biogas reactor. Examples of pre-treatment plants caninclude any one or more of the below:

a first pre-treatment tank, preferably a stripper tank for i) strippingN (nitrogen), including ammonia, from organic material, or ii) strippingN, including ammonia, from organic material collected from an additionalpre-treatment tank, wherein this first pre-treatment tank can be usedfor hydrolysing the organic material, and/or

a pre-treatment tank in the form of a lime pressure cooker forhydrolysing slurry comprising organic material, wherein said hydrolysisresults in rendering the organic material available to microbialdigestion in a bioreactor. It also eliminates, inactivates and/orreduces in number any viral or microbial organism and/or pathogenicorganism present in the slurry, or a part thereof, and/or

a pre-treatment tank in the form of a silage store for generatingensiled plant material comprising at least one or more of corn/maize,energy crops, beets, and any crop residues, and/or

a pre-treatment fermentation tank for fermenting silage and/or limepressure cooked organic material, in which the fermentation conditionsare selected from mesophilic fermentation conditions and/or thermophilicfermentation conditions.

The processing plant preferably comprises a pressure sterilization unit,a stripper and sanitation tank, and one or more fermentors for biogasproduction.

The system of the invention is capable of processing organic materialand obtaining the advantages described herein elsewhere. The systemenables methods wherein the organic material can initially be subjectedto one or more pre-treatments as listed herein above, followed by theformation of biogas by fermentation of said pre-treated organic materialat mesophile and/or thermophile conditions as described herein whilecontinuously removing volatile compounds such as e.g. ammonia from saidfermentation liquid. The removal of ammonia involves initially using ashunt and an evaporator producing cold steam. Following condensation ofcold steam comprising ammonia, the ammonia is stripped off the condensedliquid in a stripper unit. This generates a concentrated ammoniasolution useful as a fertiliser. Following the above-mentionedfermentation, additional nutrient sources such as e.g. P (phosphor) andK (potassium) can be separated and isolated in individual fractions alsouseful as fertilisers.

The at least one condensing device for condensing cold steam asdescribed herein can include two condensing devices, three condensingdevices, four condensing devices, and more than four condensing devises.In one embodiment the system comprises two condensing devices. Acondensation of cold steam comprising volatile compounds takes place ina first condensing device at a pressure below 1 bar, and a condensationof hot steam comprising volatile compounds such as e.g. ammonia takesplace in a second condensing device at a pressure of 1 bar or more.

Vapor not condensed in the first condensing device K1 at the reducedpressure can optionally be diverted to a further condensing K2 devicefor condensation by washing in a liquid counter current. The condensedvolatile compounds generated by condensation in the further condensingdevice K2 can subsequently be diverted to the stripper unit K3 e.g.together with first condensed aqueous liquid generated by condensationin said first condensing device K1. Vapor not condensed in the furthercondensing device can optionally be diverted to an air scrubber.

In one embodiment there is provided a system comprising a stripperdevice for stripping volatile compounds from a liquid medium, saidstripper device comprising:

-   -   a) a shunt to which aqueous liquid medium comprising volatile        compounds can be diverted in the form of a side stream to a        fermentor or biogas reactor,    -   b) pumps, valves and pipes for diverting aqueous liquid medium        comprising volatile compounds to the shunt from said fermentor        or biogas reactor, and    -   c) an evaporator device comprising a sample of aqueous liquid to        which heat obtained from an external heat source can be added,        wherein a reduction of the pressure in said evaporator to a        first pressure below a predetermined reference pressure        generates cold steam, and    -   d) pumps, valves and pipes for directing the cold steam        generated by the evaporator of step c) through said aqueous        liquid medium comprising volatile compounds in the shunt of the        stripper device at said pressure below a predetermined reference        pressure, thereby stripping off volatile compounds and obtaining        a cold, volatile compound-comprising steam, and    -   e) a first condensing device, and    -   f) pumps, valves and pipes for diverting said cold volatile        compound-comprising steam at said pressure below the        predetermined reference pressure to the first condensing device,        and condensing in a first condensing step in said first        condensing device said cold volatile compound-comprising steam        at said pressure below a predetermined reference pressure,        thereby obtaining a first condensed aqueous liquid medium        comprising said volatile compounds and vapor not condensed by        the first condensing device, and,    -   g) a stripper unit for stripping volatile compounds at said        predetermined reference pressure or at a second pressure higher        than said predetermined reference pressure,    -   h) pumps, valves and pipes for diverting said first condensed        aqueous liquid medium comprising volatile compounds obtained in        step f) to the stripper unit, and stripping off at least part of        the volatile compounds from said first condensed aqueous liquid        medium comprising volatile compounds by injecting hot aqueous        steam at said reference pressure or at the higher second        pressure, thereby obtaining a hot volatile compound-comprising        steam and aqueous liquid stripped off at least part of said        volatile compounds,    -   i) a second condensing device, and pumps, valves and pipes for        diverting said hot volatile compound-comprising steam to a        second condensing device, and condensing said hot volatile        compound-comprising steam, thereby obtaining a condensate        comprising volatile compounds.

In another embodiment the system comprising the stripper device forstripping volatile compounds comprises:

-   -   a) a shunt S to which aqueous liquid medium comprising volatile        compounds can be diverted or shunted in the form of a side        stream,    -   b) pumps, valves and pipes for diverting aqueous liquid medium        comprising volatile compounds such as e.g. ammonia to the shunt,        and    -   c) an evaporator device E for producing steam from a sample of        warm aqueous liquid diverted to the evaporator by reducing the        pressure below a predetermined reference pressure, and    -   d) pumps, valves and pipes for directing a cold steam generated        by the evaporator E of step c) through said liquid medium        comprising volatile compounds in the shunt S of the stripper        device by said pressure below a predetermined reference        pressure, thereby stripping off volatile compounds and obtaining        a cold, volatile compound-comprising steam, and    -   e) a first condensing device and a second condensing device, and        optionally a further condensing device,    -   f) pumps, valves and pipes for diverting said cold volatile        compound-comprising steam at said pressure below a predetermined        reference pressure to the first condensing device, and        condensing in a first condensing step in said first condensing        device said cold volatile compound-comprising steam by said        pressure below a predetermined reference pressure, thereby        obtaining a first condensed aqueous liquid medium comprising        said volatile compounds and vapor not condensed by the first        condensing device, and    -   g) optionally pumps, valves and pipes for diverting said vapor        not condensed by the first condensing device to the further        condensing device, when present, and removing a substantial part        of the remaining volatile compounds from said vapor not        condensed by the first condensing device, said removal involving        washing the vapor in a counter current of aqueous liquid,        thereby obtaining an aqueous liquid fraction comprising volatile        compounds and vapor not condensed by the further condensing        device, and    -   h) pumps, valves and pipes for diverting said first condensed        aqueous liquid medium comprising volatile compounds obtained in        step f) and optionally also said aqueous liquid fraction        comprising volatile compounds obtained in step g) to a stripper        unit, and stripping off the volatile compounds from said first        condensed aqueous liquid medium comprising volatile compounds        such as e.g. ammonia and optionally also from said aqueous        liquid fraction comprising volatile compounds such as e.g.        ammonia by heating at a higher second pressure, thereby        obtaining a hot volatile compound-comprising steam and aqueous        liquid stripped off volatile compounds, and    -   i) pumps, valves and pipes for diverting said hot volatile        compound-comprising steam to a second condensing device, and        condensing said hot volatile compound-comprising steam, thereby        obtaining a condensate of volatile compounds.

The term “aqueous liquid stripped off at least part of volatilecompounds” as used herein above shall denote an aqueous liquid mediumcomprising a reduced concentration of said volatile compound as comparedto the concentration of the volatile compound in the aqueous liquidmedium initially diverted to the shunt. A reduced concentration shalldenote a reduction of at least 2 fold, such as 3 fold, for example 4fold, such as 5 fold, for example 6 fold, such as 7 fold, for example 8fold, such as 9 fold, for example 10 fold, such as 15 fold, for example20 fold, such as 25 fold, for example 40 fold, such as 60 fold, forexample 80 fold, such as 100 fold, or even more.

When the volatile compound is ammonia, the second condensed aqueousliquid (obtained from condensation of the hot vapor generated by theend-stripper unit) preferably comprises less than 10000 ppm ammonia,such as e.g. 5000 ppm ammonia, for example 4000 ppm ammonia, such ase.g. 3000 ppm ammonia, for example 2000 ppm ammonia, such as e.g. 1000ppm ammonia, for example 800 ppm ammonia, such as e.g. 700 ppm ammonia,for example 600 ppm ammonia, such as e.g. 500 ppm ammonia, for example400 ppm ammonia, such as e.g. 300 ppm ammonia, for example 250 ppmammonia, such as e.g. 200 ppm ammonia, for example 150 ppm ammonia, suchas e.g. 100 ppm ammonia, for example 80 ppm ammonia, such as e.g. 70 ppmammonia, for example 60 ppm ammonia, such as e.g. 50 ppm ammonia, forexample 40 ppm ammonia, such as e.g. 30 ppm ammonia, for example lessthan 20 ppm ammonia, such as less than 10 ppm ammonia.

The term “volatile compound” is used to describe any compound capable ofbeing stripped off an aqueous liquid by heating said liquid, preferablyheating combined with a reduced pressure, e.g. a pressure below 1 bar.The volatile compounds can be e.g. ammonia and/or methane or methanecarrying gas.

The flows and concentrations illustrated in the figures constitute onerealistic example of operating conditions of the shunt when coupled to abiogas reactor.

The stripper device and its components are described in more detailbelow in relation to stripping off volatile compounds such as e.g.ammonia from aqueous liquids.

Part of the volatile compounds-such as e.g. ammonia comprised in theaqueous liquid is stripped from the liquid in a stripper systemcomprising a shunt as illustrated in the figures. The shunt can beconnected to a plant comprising e.g. a fermentor and/or a biogasreactor. Any plant generating liquids comprising volatile compounds suchas e.g. ammonia during the operation of the plant is within the scope ofthe present invention. Examples include, but is not limited to,fermentors, biogas reactors, and plants generating waste water from theproduction of e.g. fertilisers.

The working principle of this aspect of the invention is that a fractionof the active biomass in the process tank is diverted to the shunt wherethe inhibitory substance such as e.g. ammonia is removed. It isessential that the various microbial consortia are left unaffected bythe treatment because the digestion shall continue when the biomass issubsequently returned to the bioreactor. A substantial killing of theslow growing methanogenic bacteria would be lethal to the biogasprocess.

The shunt thus controls the concentration of the inhibitory substancesuch as e.g. ammonia in the bioreactor at a level sub critical to theanaerobic digestion and the operation of the bioreactor in general.

Accordingly, one aspect of the invention is directed to a method forreducing the concentration of volatile compounds such as e.g. ammonia ina liquid by stripping off at least part of the volatile compounds fromthe liquid, said method comprising the steps of

-   -   a) providing a liquid medium comprising volatile compounds, and    -   b) diverting said liquid medium comprising volatile compounds to        a shunt operationally linked to a steam and heating source such        as an evaporator and a heat source, respectively, and a        condensing device,    -   c) obtaining cold steam in the evaporator by reducing the        pressure of the heating source below a predetermined reference        pressure, and    -   d) directing said cold steam through said liquid medium        comprising volatile compound in the shunt of the stripper device        at said pressure below a predetermined reference pressure,        thereby stripping off volatile compound and obtaining a cold        volatile compound-comprising steam, and    -   e) diverting said cold volatile compound-comprising steam at        said pressure below a predetermined reference pressure to a        first condensing device, and    -   f) condensing in a first condensing step said cold volatile        compound-comprising steam at said pressure below a predetermined        reference pressure, thereby obtaining a first condensed aqueous        liquid medium comprising volatile compound, and    -   g) diverting said first condensed aqueous liquid medium        comprising volatile compound to a stripper unit, and    -   h) stripping off the volatile compounds from said first        condensed aqueous liquid medium comprising volatile compounds by        heating said first condensed aqueous liquid in said stripper        unit at a higher second pressure, and    -   i) obtaining a liquid with a reduced concentration of volatile        compounds.

In this aspect the liquid medium comprising volatile compounds such ase.g. ammonia, and optionally also amines, can be any such liquid asdescribed herein elsewhere. The aqueous liquid can be water or anyaqueous solution suitable for being diverted e.g. to a biomass in afermentor. The method can include the further step of diverting from thefirst condensing device condensed aqueous liquid medium comprisingammonia to a further condensing device as described herein below in moredetail.

In yet another embodiment there is provided a system for stripping ofammonia from a liquid, said system comprising

-   -   an evaporator for heating a sample of liquid, preferable a        sample of aqueous liquid at a pressure below a predetermined        reference pressure, to obtain a cold steam at a temperature        below the boiling temperature of said liquid, and    -   a stripper device for stripping ammonia from a liquid medium        comprising ammonia by diverting said cold steam through said        liquid medium comprising ammonia at said pressure below a        predetermined reference pressure, obtaining a cold        ammonia-comprising steam,    -   wherein said liquid medium comprising ammonia is preferably a        liquid medium from a bioreactor, such as a bioreactor for        treating organic waste, in particular a bioreactor for treating        animal manure and/or plant parts and/or slaugtherhouse waste,        including meat and bone meal, said stripper unit comprising    -   a first condensing device for condensing said cold        ammonia-comprising steam at said pressure below a predetermined        reference pressure, obtaining a first condensed aqueous liquid        medium comprising ammonia, and    -   a stripper unit for stripping said first condensed aqueous        liquid medium comprising ammonia for ammonia by heating at a        higher second pressure.

The system can further comprise at least one vapor evacuation pumps forevacuating vapor for producing said pressure below a predeterminedreference pressure,

In yet another embodiment there is provided a stripper devicecomprising:

(A) a first stripping unit, said first unit comprising:

-   (a) a stripping container for producing a vapor of volatile    components from the liquid at a reduced pressure below a    predetermined reference pressure;-   (b) a first condensing device for condensing said vapor of volatile    components from said stripping container at said reduced pressure;-   (c) a phase separator for separating said condensed volatile    components and said vapor of volatile components from said first    condenser into a condensed phase and a vapor phase at said reduced    pressure; and-   (d) at least one vapor evacuation pumps for evacuating said vapor    for producing a reduced pressure below said reference pressure; said    vapor evacuation pumps being positioned down stream said first    condenser; and    (B) a second stripping unit, said unit comprising:-   (e) a second stripping container for producing a vapor of volatile    components from said condensed phase at said predetermined reference    pressure; and-   (f) a second condensing device for condensing said vapor of volatile    components at said predetermined reference pressure,    whereby it is obtained that heating media of low-value can be used    for heating of the volatile components in the vacuum stripping    process.

Preferred embodiments of the present invention are disclosed hereinbelow in more detail.

The stripper device can be operably linked to a processing plant such asa bioreactor and/or any pre-treatment plant as disclosed hereinelsewhere.

Further, allowing a first condensation process for producingintermediate concentrations of said volatile components; simple coolingmedia can be used in the condenser for condensing the first strippedvolatile components.

Also, since main stream vapor compressor can be avoided, simpler andless expensive vapor compressors can be used.

Generally, the reduced pressure in the system of first stripping column,first condenser, and phase separator, can be any suitable pressureensuring that volatile components are kept in their respective phases atthe prevailing pressures and temperatures.

However, it may be desirable to have different operating pressures atthe different units.

In a preferred embodiment, said first condenser, said phase separatorhave a pressure at or above said reduced pressure whereby it is obtainedthat volatile products are removed in a higher concentration using lessheat but which volatile products can still be condensed using coolingwater.

Generally, the liquid to be treated contains dissolved gasses, which mayevaporate at the reduced pressure. Removal of these gasses is necessaryfor maintaining the reduced pressure.

Consequently, in a preferred embodiment, said at least one vaporevacuation pumps is connected to said phase separator whereby it isobtained that dissolved gasses can be removed.

The vapor evacuation pumps can be any suitable pumps for pumping thegasses in question. Consequently, in a preferred embodiment, said atleast one vapor evacuation pumps is a displacement vacuum pump wherebyremoval of gas using a relatively inexpensive energy compressor with lowenergy demand is obtained.

The stripping container can be any container suitable for containing theliquid and volatile components in question as well as for operating atthe required temperature and pressure.

Consequently, in a preferred embodiment, said first stripping containercomprises; a container, an inlet, a heating means, a vapor outlet, aresidue outlet, and internals, e.g. loose and fixed packing materialsand plate-providing means such as a strainer; said container, inlet,vapor outlet, residue outlet, and internals being adapted to operate ata reduced pressure below said reference pressure.

In a preferred embodiment, said reference pressure is atmosphericpressure whereby particular simple and readily available equipment, inparticular the second stripping container can be applied.

A person skilled in the art can select means for transportation ofliquids and gasses.

For transportation of liquids any suitable pump meeting the physical andchemical properties of the liquid to be treated can be used. Thus, asuitable liquid pump is typically adapted to function with respect toviscosity, temperature and pressure of the liquid. Also, corrosiveproperties of the liquid and content of solid particles affect thechoice of a pump of suitable construction and material. Generally,suitable liquid pumps include centrifuges, plunger pumps anddisplacement pumps, e.g. rotating displacement pumps.

Specific liquid pumps are preferably centrifugal pumps.

For transportation of gases any suitable pump meeting the physical andchemical properties of the gasses to be treated can be used. Thus, asuitable gas pump is typically selected to function with respect torequired pressure and capacity, but also with respect to temperature,purity, energy demand, price, and corrosion properties. Generally,suitable gas pumps include blowers, and compressors.

Gas pumps used for providing a reduced pressure include vacuum pumpssuch as plunger pumps, displacement pumps and rotation pumps.

Specific vacuum pumps comprise preferably rotary displacement pumps.

In a preferred embodiment, the system comprises means for production ofa combustion gas for combustion in a combustion engine whereby it isobtained that any heat produced from the combustion gas as a low-valuedcooling media can be used as heating medium.

In a preferred embodiment, the system comprises means f or convertingheat produced by combustion of said combustion gas to produce a vapor ofvolatile components in a stripping container of said vapor strippingapparatus, in particular according to the invention.

Generally, liquid comprising volatile components can be treatedaccording to the invention. However, it is desired that the liquidexhibits certain properties. Consequently, the liquid can have beensubjected to various treatments before being entered into the firststripping container.

In a preferred embodiment relating to the treatment of liquids ofmanure, said treatment comprises wholly or partial hydrolysis,biological degassing, and mechanical separation of solid matter wherebyit is obtained that the gas production (and in this way the energyproduction) is maximized, and that organic products which might harm theprocess are minimized.

The systems described herein above can further comprise a first phaseseparator operating at said pressure below a predetermined referencepressure, for separating said first condensed aqueous liquid mediumcomprising ammonia and vapor not condensed by the first condensingdevice.

The systems can comprise a further condensing device, whereto said vapornot condensed by the first condensing device is diverted at saidpressure below a predetermined reference pressure, removing asubstantial part of the remaining ammonia by washing in a countercurrent of aqueous liquid medium, and obtaining a aqueous liquidfraction comprising ammonia and vapor not condensed by the furthercondensing device.

The systems can also comprise a second condensing device condensing saidhot ammonia-comprising steam by cooling, thus obtaining a secondcondensed aqueous liquid medium comprising ammonia.

The second condensing device is preferably two heat exchangers coolingsaid hot ammonia-comprising steam to generate said second condensedaqueous liquid medium comprising ammonia in two steps, thus directingthe obtained heat to said evaporator to heat liquid in said evaporator.The heat exchangers can be connected to heating means outside of thesystem.

The system can further comprise a second phase separator for separatingsaid second condensed aqueous liquid medium comprising ammonia and vapornot condensed by the condensing device.

The systems can further comprise at least one air scrubber for cleaningsaid vapor not condensed by the condensing device(s), as well as coolingtower(s) for cooling aqueous liquid by evaporation to the atmosphere,and preferably also a storage container for storing said secondcondensed aqueous liquid medium comprising ammonia.

The system can comprise conventional connecting means, such as pipes,tubes cylinders, pipelines, hoses, hosepipes, canals, and ducts,preferably for connecting or operationally linking any one or more of:

one or more bioreactor(s) with the stripper device, and connecting inthe stripper device itself:

-   the evaporator with the shunt, and-   the shunt with the first condensing device, and-   the first condensing device with the cooling tower, and-   the first condensing device with the first phase separator, and-   the first phase separator with the further condensing device, and-   the first phase separator with the stripper unit, and-   the further condensing device with the air scrubber, and-   the further condensing device with the stripper unit, and-   the stripper unit with the second condensing device, and-   the further condensing device with the evaporator, and-   the further condensing device with a heat exchanger, and-   the second condensing device with the second phase separator, and-   the second condensing device with the evaporator, and-   the second condensing device with the storage container, and-   the heat exchangers with the evaporator, and-   the heat exchangers with the cooling tower.

The pumps of the system are capable of pumping liquid medium or vaporthrough said connecting means.

In another embodiment there is provided a mobile unit comprising asystem for stripping ammonia from a liquid medium as described herein.The stripper device of the mobile unit is illustrated in FIG. 2.

Process Plants Linked to the Stripper Device

The following sections disclose specific embodiments of the inventionwherein the aforementioned stripper device comprising a shunt andcondensing device(s) is operationally connected to a processing plantfor processing organic material. The organic material can comprise e.g.animal manure, such as pig and/or cow manure, and/or animal slurry, suchas pig and/or cow slurry, and/or plant parts, wherein said plant partscomprise one or more of straw, crops, crop residues, silage, energycrops. Another example of material capable of being processed inconnection with the present invention is animal carcasses or fractionshereof, slaughterhouse waste, meat and bone meal, blood plasma, and thelike, originating from animals, as well as risk- and no-risk materialwith respect to the potential presence of BSE-prions or other prions.

After an optional pre-processing or pre.treatment depending on the kindof material used, said material is diverted to e.g. a biogas reactorwherein said organic material is fermented at mesophilic or thermophilicconditions, wherein said fermentation generates biogas.

The fermentor and/or biogas reactor can be further operably linked toadditional units such as e.g. any one or more of a lime pressure cookerand a pre-treatment plant, as described in more detail herein below.

Fermenting organic material in a biogas fermentor can involvefermentation processes in one or more plants.

In one embodiment, the biogas production is performed in two plants byanaerobic bacterial fermentation of the organic material, initially byfermentation at thermophilic temperatures in a first plant, followed bydiverting the thermophilicly fermented organic material to a secondplant, wherein fermentation at mesophilic temperatures takes place.

The thermophilic reaction conditions preferably include a reactiontemperature ranging from 45° C. to 75° C., such as a reactiontemperature ranging from 55° C. to 65° C., such as about 60° C.

The mesophilic reaction conditions preferably include a reactiontemperature ranging from 20° C. to 45° C., such as a reactiontemperature ranging from 30° C. to 35° C. The thermophilic reaction aswell as the mesophilic reaction is preferably performed for about 5 to15 days, such as for about 7 to 10 days.

Any potential foam formation can be reduced and/or eliminated by theaddition of polymers (polyglycols), silozanes, fatty acids, and/or plantoils, and/or one or more salts, preferably plant oil in the form of rapeoil. The salts preferably comprise or essentially consist of CaO and/orCa(OH)₂.

A desirable flocculation of substances and particles during biogasproduction is preferably achieved by the addition of calcium-ionscapable of forming calcium-bridges between organic and inorganicsubstances in solution or suspension, wherein said calcium-bridgesresulting in the formation of ‘flocks’ of particles. The addition ofcalcium-ions further results in the precipitation of orthophosphates,including dissolved (PO₄ ³⁻), which is preferably precipitated ascalcium phosphate Ca₃(PO₄)₂ wherein the precipitated calcium phosphatepreferably remains suspended in a slurry.

The obtained biogas can be diverted to a gas engine capable of producingheat and/or electricity. The heat can be used to heat a lime pressurecooker and/or the fermentation plant and/or a N stripper reactor and/orthe one or more biogas plant(s) and/or an animal house(s) and/or a humanresidence and/or heating aqueous liquid to be used in a household orhuman residence. The electricity can be diverted and sold to acommercial net for distributing electricity. In one preferredembodiment, the remaining N stripped, sterilised and fermented organicmaterial is spread on agricultural fields.

Prior to fermentation in the biogas plants, the organic material can betreated in a lime pressure cooker. The lime pressure cooker of thesystem is preferably an apparatus, which is initially capable of cuttingthe organic material into segments and subsequently capable of divertingthe segmented organic material to a chamber wherein said segmentedorganic material is heated and simultaneously exposed to a high pressuredue to the elevated temperature. The organic material to be treated inthe lime pressure cooker is added an amount of lime, including CaOand/or Ca(OH)₂ prior to or after entry into the lime pressure cooker.

Preferably CaO is added to the lime pressure cooker in an amount of from25-100 g per kg dry matter in the organic material. The system operatesat a temperature of between 100° C. and 220° C., such as e.g. 180° C. to200° C. The temperature is aligned according to the organic material tobe treated, a higher temperature is chosen the higher the content ofcellulose, hemicellulose and lignin is in the organic material, or ahigher temperature is chosen according to the risk of infectiousmicrobial organism or pathogenic compounds including BSE prions in theorganic material such as e.g. meat and bone meal.

The pressure in the lime pressure cooker is preferably between from 2 topreferably less than 16 bar, such as from 4 to preferably less than 16bar, for example from 6 to preferably less than 16 bar, such as from 10to preferably less than 16 bar. The system operates at the elevatedtemperature for about 5 to 10 minutes, but longer treatment times canalso be used.

N including ammonia stripped in the lime pressure cooker is preferablycollected and diverted to a column and absorbed as described hereinelsewhere.

Prior to fermentation in the biogas plants, the organic material in theform of silage such as e.g. maize, energy crops, beets, and/or any cropresidues, can be diverted to a mesophilic or thermophilic fermentationtank, before the material is further diverted to the stripper tank.

The lime pressure cooked organic material can also be diverted to amesophilic or thermophilic fermentation tank, before the material isdiverted to the stripper tank.

The invention also facilitates the optimization of the fermentation ofthe organic material and the production of biogas by providing apre-treatment plant comprising facilities for stripping N includingammonia and/or performing alkaline hydrolysis under predeterminedprocess parameters, including pH level, temperature, aeration, duration,foam inhibition and flocculation of suspended material.

In another embodiment of the invention the method ensures optimisedconditions for the population of microbial organisms contained in thebiogas producing fermenters. This is achieved by e.g. divertingsterilised or sanitised slurry from the stripper tank to at least afirst biogas fermenter, wherein said sterilised or sanitised slurry donot inhibit or harm the population of biogas producing microbialconsortia in the fermenter. In particular, organic material from which Nincluding ammonia is stripped, can be diverted to a biogas reactor inwhich the fermentation conditions supports a mesophilic fermentation.Once the organic material has been subjected to a mesophilicfermentation, the organic material is preferably diverted to anotherbiogas reactor of the system, in which the fermentation conditions arecapable of supporting a thermophilic fermentation.

The organic material fermented in the biogas plants may also constituteorganic material obtained from animal houses. In one embodiment theorganic material from the animal houses is diverted to the stripper tankbefore fermentation in the biogas fermentors. The animal organicmaterial is preferably from farm animals including cows, pigs, cattle,horses, goats, sheep and/or poultry, and the like. The organic materialfrom animal houses may constitute solid and/or liquid parts selectedfrom manures and slurries thereof, and animal carcasses or fractionsthereof, such as e.g. meat and bone meal.

In the fermentation process in the biogas fermentors, the bacteriapreferably produce mainly methane and a smaller fraction of carbondioxide when fermenting the organic material. When the content ofammonia in the liquid in the biogas fermentor reaches a level aboveabout 5 kg/m³, the bacteria population is negatively affected to such adegree that the fermentation process is severely hampered. The influenceof the ammonia can be controlled by using the present invention so thatthe ammonia level is kept below about 4 kg/m³, such as a level of about3 kg/m³, or lower if desirable.

In an embodiment of the invention the ammonia content of thefermentation liquid of a biogas fermentor is lowered by stripping offpart of the ammonia from the fermentation liquid in a shunt as describedherein elsewhere in more detail, and the fermentation liquid stripped ofpart of the ammonia can subsequently be returned to the biogasfermentor.

In addition to the aforementioned pre-treatment plans the stripperdevice comprising the shunt, the condensing device(s) and the stripperunit, can also be operably connected to a pre-shunt degassing unit.

Biogas consists of methane and carbon dioxide. The biogas, which isproduced within the active biomass, i.e., a slurry of micro-organisms,substrate, dissolved salts, nutrients, gasses etc. continuously escapesfrom the biomass slurry and is subsequently diverted to, e.g., amotor-generator unit.

The solubility of methane gas in water is of the order of 2×10⁻⁵expressed as mole fraction at a temperature of about 300K, while thesolubility of carbon dioxide is of the order of 5×10⁻⁴ at 300 K.

Hence, at the operating conditions of bioreactors and in case ofsufficient stirring and hydraulic residence time only traces of theproduced methane and carbon dioxide gas is dissolved in the slurry.However, it cannot be excluded that micro-bubbles are trapped oradsorbed in the slurry and some practical evidence suggest that of theorder of 5-10% of the total produced biogas may be trapped in thebiomass slurry.

It is important that this methane is removed from the slurry before itenters the shunt. If not, the methane gas would escape to theatmosphere, which is unwanted because it is a potent greenhouse gas andbecause it effectively reduces the biogas to be utilized in, e.g., themotor-generator plant. The presence of excess methane and carbon dioxidewould also cause some difficulties to the stripping of ammonia andrequire higher vacuum capacity. If CO₂ were removed, on the other hand,the ammonia stripping would benefit from a slight pH increase accordingto the equations:CO₂+H₂O=H₂CO₃;  a)H₂CO₃=H⁺+HCO₃ ⁻;  b)HCO₃ ⁻=H⁺+CO₃ ⁻⁻;  c)pH=pKa+log [HCO₃ ⁻]/[H₂CO₃],  d)from which appears, that removal of CO₂ or H₂CO₃ will shift the chemicalequilibrium to the left resulting in consumption of H⁺ ions. Accordingto equation d) the normal concentrations of HCO₃ ⁻ and H₂CO₃ are 25×10⁻³M and 1.25×10⁻³ M at pH 7.4, which is a typical pH of biomass slurries.

In order to remove dissolved methane CH₄ (aq) and trapped methane CH₄(g) from the biomass slurry it shall pass a pre-shunt degassing unit,which consists of a vacuum tank equipped with a disperser. Where thevacuum in the shunt is between 0.1-0.2 bars, the vacuum in the pre-shuntshall by between 0.6-0.8 bars. Such vacuum is sufficient to removemethane and carbon dioxide and will at the same time prevent ammoniafrom being stripped off the slurry in any significant quantities.

The methane and carbon dioxide is subsequently diverted to themotor-generator unit together with biogas from the bioreactors.

A number of organic substances in biomass slurry may cause foaming,which gives rise to operational difficulties of bioreactors etc. Lipids,proteins, fatty acids and extra cellular polymeric substances as well asfilamentous microorganisms may cause foaming. In connection with highgas formation the risk of foaming is substantial. Thus, the ammoniastripping in the shunt (and also the stripping of other dissolvedgasses) may stimulate foam formation.

However, if prone to foaming this will also occur in the pre-shuntdegasser. This unit may therefore be equipped with a mechanical foambreaker such as a centrifuge or cyclone. In a cyclone the rotationalforce is superimposed on the centripetal force and foam entering acyclone is therefore thrown at the wall under the influence of theseforces, while the gas (methane and carbon dioxide) is forced into thecentre of the cyclone and discharged through an outlet pipe (and, e.g.,to a motor-generator plant). The condensed liquid phase may becirculated back in to the pre-shunt vessel or perhaps back into thebioreactor.

Introducing the pre-shunt degasser possibly equipped with a mechanicalfoam breaker thus substantially reduces the foaming potential of thebiomass slurry and provides for an optimal performance of the shunt.

Chemical anti foaming agents may also be considered, however, these mayinterfere with the microbiological process in the bioreactor if notcarefully selected.

Evaporator

The shunt of the stripper device is connected to a heating unitpreferably in the form of an evaporator. In said evaporator aqueousliquid is heated to obtain warm aqueous liquid, where the heat isprovided through an external source. Cold steam is produced by means ofvacuum over the surface of the warm aqueous liquid, thus lowering thetemperature of the liquid and thereby using the heat energy of theliquid.

In a preferred embodiment of the invention, the temperature of theaqueous liquid in the evaporator is about 60-80° C., such as 60-75° C.,for example such as 60-70° C., such as 65-75° C., for example such as65-80° C., such as 65-75° C., for example 68-72° C., such as about 70°C.

In another preferred embodiment of the invention, the pressure of theevaporator is about 200 to 500 hPa, such as about 200 to 450 hPa, forexample about 200 to 400 hPa, such as about 200 to 380 hPa, for exampleabout 250 to 380 hPa, such as about 250 to 370 hPa, for example about250 to 360 hPa, such as about 270 to 360 hPa, for example about 270 to350 hPa, such as about 270 to 340 hPa, for example about 270 to 330 hPa,such as about 270 to 320 hPa, for example about 280 to 320 hPa, such asabout 290 to 320 hPa, for example about 300 to 320 hPa, such as about310 hPa.

In a preferred embodiment the cold steam for the stripping process isproduced by means of vacuum over a surface of warm aqueous liquid. Thistakes place in the evaporator. The temperature of the aqueous liquid inthe evaporator is preferably maintained by means of e.g. cooling aqueousliquid from a motor-generator unit in a biogas plant, or alternatively,from any other waste heat source or motor-generator. The waste heat, inthe form of warm aqueous liquid, can be present at temperatures as lowas 60-70° C. Aqueous liquid at higher temperatures may also be used,however, in such cases the vapor has to be cooled to temperaturessuitable to the microorganisms in the biogas reactor, i.e., at a maximumof 65° C. and preferably at a temperature close to the operatingtemperature of the bioreactor.

The system preferably comprises pipe lines constituting a closed systempreventing or leading to a reduction in emissions of any one or more ofdust, microbial organisms, ammonia, air, liquid or any other constituentwithin the system.

In a preferred embodiment said pressure below a predetermined referencepressure is obtained in the evaporator, the shunt, the first condensingdevice and the optional further condensing device.

In a further preferred embodiment said pressure below a predeterminedreference pressure is preferably 0.1 to less than 1.0 bar, such as 0.1to 0.4 bar, and more preferably from about 0.1 to about 0.35 bar.

In one preferred embodiment said pressure is about 0.27 bar to 0.35 bar,such as about 0.29 to about 0.33 bar, for example about 0.31 bar in theevaporator, and about 0.12 to about 0.20 bar, for example from about0.14 to about 0.18, such as about 0.16 bar in the shunt, and from about0.16 bar to about 0.24 bar, for example from about 0.18 bar to about0.22 bar, such as about 0.20 bar in the first condensing device and inthe optional further condensing device.

The aqueous liquid medium heated in the evaporator to produce said coldsteam can be any aqueous liquid source preferably with a maximum ammoniaconcentration of 3 kg ammonia per tonnes of liquid, such as a maximum 2kg ammonia per tonnes of liquid, for example a maximum 1 kg ammonia pertonnes of liquid, such as a maximum 0.5 kg or less ammonia per tonnes ofliquid.

In a preferred embodiment said aqueous liquid source is tap water, wasteaqueous liquid, or aqueous liquid from a biogas production.

The heating process in the evaporator is conducted by using heatexchangers reusing heat from machines, from warm waste aqueous liquid orfrom aqueous liquid of a cooling devices, such as from the firstcondensing device or from the second condensing device of a plant asdescribed herein.

Condensing Device(s)

The present invention is disclosed herein below with respect to one ormore condensing devices for condensing steam and vapors comprisingvolatile compounds including ammonia and volatile amines.

The condensing process steps can include the use of a first condensingdevice and optionally also a further condensing device for condensingcold steam comprising volatile compounds, and a second condensing deviceoperationally linked to a stripper unit, wherein said second condensingdevice condenses steam comprising volatile compounds at a pressure at orabove said reference pressure.

In one embodiment the invention provides for the generation of a vaporcomprising volatile compounds including e.g. ammonia, which vapor is notcondensed by the first condensing device, and said vapor not condensedby the first condensing device can subsequently be diverted to a furthercondensing device at said pressure below a predetermined referencepressure, removing at least a substantial part of the remaining ammoniaas possible from said vapor not condensed by the first condensingdevice. This is possible by including a washing step exploiting acounter current of aqueous liquid, said washing step and saidcondensation resulting in an aqueous liquid fraction comprising ammoniaand vapor not condensed by the further condensing device.

The aqueous liquid fraction comprising ammonia obtained from the furthercondensing device can be diverted to the stripper unit, where, togetherwith the first condensed aqueous liquid medium comprising ammonia alsodiverted to said stripper unit, ammonia is stripped off by heating atsaid higher second pressure, and obtaining a hot ammonia-comprisingsteam and aqueous liquid stripped off at least part of said ammonia.

The hot ammonia-comprising steam obtained as described hereinimmediately above is diverted to a second condensing device capable ofcondensing said hot ammonia-comprising steam at or above said referencepressure, thereby obtaining a further condensed aqueous liquid mediumcomprising ammonia and optionally also vapor not condensed by the secondcondensing device.

The vapor not condensed by the further condensing device and/or thesecond condensing device can be directed to an air scrubber or releaseddirectly to the atmosphere.

The temperature of said first condensed aqueous liquid medium comprisingammonia is preferably 15-35° C., such as 20-30° C., for example 23-28°C., such as about 25° C.

The temperature of said counter current of aqueous liquid in the thirdcondensing device is preferably 15-35° C., such as 20-30° C., forexample 23-28° C., such as about 25° C.

The temperature of said first condensed aqueous liquid medium comprisingammonia and of said aqueous liquid fraction comprising ammonia in thestripper unit is preferably 80-170° C., such as 85-130° C., for example90-110° C., such as about 100° C.

The temperature of said hot ammonia-comprising steam when leaving thestripper unit is preferably 50-110° C, such as 60-100° C, for example70-90° C., such as about 80° C.

The temperature of said ammonia concentrate is preferably 15-45° C.,such as 20-40° C., for example 25-35° C., such as about 30° C.

The aqueous liquid medium preferably comprises an amount of from 2.5 to5 kg ammonia per m³ (cubic meter), such as 2.6 to 4 kg ammonia per m³,such as 2.7 to 3.5 kg ammonia per m³, for example 2.8 to 3.2 kg ammoniaper m³, such as 2.9 to 3.1 kg ammonia per m³, such as about 3.0 kgammonia per m³.

The liquid medium comprising ammonia is preferably liquid medium furthercomprising organic materials, preferably a liquid from a bioreactor,such as a bioreactor for treating organic waste, in particular abioreactor for treating manure, including swine manure, and/or meat andbone meal.

The liquid medium comprising ammonia enters the shunt in one end, isdiverted through the shunt simultaneously with the addition of coldsteam, and the liquid medium subsequently leaves said shunt having areduced concentration of ammonia.

The cold ammonia-comprising steam from the shunt preferably comprisesammonia in a concentration of about 0.5 to 10% ammonia, for example 0,5to 8% ammonia, such as about 0.5 to 7% ammonia, for example about 0.5 to6% ammonia, such as about 0.5 to 5% ammonia.

The second condensed aqueous liquid medium preferably comprises ammoniain a concentration of about 10-40%, such as 15-35%, for example such as20-30%, such as about 25%.

The liquid with a reduced concentration of ammonia resulting fromstripping off ammonia in the shunt preferably comprises ammonia in aconcentration of less than 3 kg ammonia per tonnes of liquid, such asabout 2.5 kg ammonia per tonnes of liquid, for example about 2.0 kgammonia per tonnes of liquid, such as about 1.5 kg ammonia per tonnes ofliquid, for example about 1.0 kg ammonia per tonnes of liquid, such asless than about 2.0 kg ammonia per tonnes of liquid, for example lessthan 1.0 kg kg ammonia per tonnes of liquid.

The liquid with a reduced concentration of ammonia is preferably shunted(back) to a bioreactor, such as to the bioreactor from where said liquidmedium comprising ammonia was initially obtained, or to a bioreactor inconnection with the bioreactor from where said liquid medium comprisingammonia was initially obtained.

It is important that the liquid having a reduced concentration ofammonia being diverted back to a bioreactor has no negative influence onthe microorganisms in the bioreactor. It must not impair growth orenzyme activity of the microorganisms. The bioreactor is preferablymesophilic or thermophilic.

Biomasses of low and high contents of protein can be fermented in thebioreactor. Examples of biomasses with a high contents of protein can beanimal bi-products e.g. meat and bone meal, vegetable protein, molassesand vinasse. The amount of meat and bone meal fermented in thebioreactor preferably comprises more than 2.5%, such as more than 5%,preferable more than 10%, such as more than 15%, such as more than 20%,such as more than 25% of the total biomass by weight. One use of thecondensed aqueous liquid with a high ammonia concentration is for acommercial fertiliser.

The biomasses with high contents of protein, including meat and bonemeal can be initially diverted to one or more pre-treatment plantsbefore fermentation in said bioreactor, wherein said pre-treatmentplants preferably comprises:

a first pre-treatment tank, preferably a stripper tank for stripping N(nitrogen), including ammonia, from the biomasses, and/or

a second pre-treatment tank, preferably a lime pressure cooker forhydrolysing biomasses, wherein said hydrolysis results in eliminating,inactivating and/or reducing in number any viable microbial organismsand/or pathogenic substances present in the biomasses, or a partthereof, and/or

at least one tank, preferably a silage store for generating ensiledplant material comprising at least one or more of corn/maize, energycrops, beets, and any crop residues, and/or

at least one second tank, preferably a pre-treatment fermenting tank toferment silage and/or lime pressure cooked organic material, in whichthe fermentation conditions are selected from mesophilic fermentationconditions and/or thermophilic fermentation conditions.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the main processes of one embodiment of the presentinvention.

R: R denotes a bioreactor, in this case a biogas reactor with anoperating temperature of about 55° C. The ammonia concentration in thebiogas reactor shall be held at a maximum of about 3 kg NH₃ per m³.

S: The shunt S typically operates at a pressure below a predeterminedreference pressure, preferable at a pressure below the atmosphericpressure. The liquid to be stripped for a fraction of its ammoniacontent is diverted from R to the S by means of a pump or inlet valve.During the passage of the liquid through the S, cold steam is directedthrough the liquid. The stripped liquid medium comprising liquid with areduced concentration of ammonia is subsequently pumped back to thebioreactor R or to another bioreactor R2 in connection with thebioreactor R.

E: The cold steam for the stripping process is produced in theevaporator E by means of vacuum over a surface of warm aqueous liquid.The temperature of the aqueous liquid in the evaporator E is preferablymaintained by means of e.g. cooling aqueous liquid from amotor-generator unit in a biogas plant, or alternatively, from any otherwaste heat source. The waste heat, in the form of warm aqueous liquid,can be present at temperatures as low as 60-70° C. Aqueous liquid athigher temperatures may also be used, however, in such cases the vaporhas to be cooled to temperatures suitable to the microorganisms in thebiogas reactor, i.e., at a maximum of 65° C. and preferably at atemperature close to the operating temperature of the bioreactor.

K1: In the shunt S, where cold steam is directed through the liquid andhereby removing at least part of its ammonia content, the producedmixture of steam and ammonia comprising cold ammonia-comprising steam isdiverted from S to a first condensing device K1, where the coldammonia-comprising steam is condensed to a first condensed aqueousliquid medium comprising ammonia which is a dilute ammonia/aqueousliquid solution by means of cooling aqueous liquid in a cooling tower.

K1 can be split in two parts (as can also K2 and K4) in order for thefirst part to produce relatively warm cooling aqueous liquid and thesecond part relatively cold cooling aqueous liquid. The relatively warmcooling aqueous liquid may in both cases be used directly in the shuntor any other heating purpose.

The cold cooling aqueous liquid from K1 and K4 having a temperature of32° C. or somewhat less may be used in a heat pump to generate warmaqueous liquid at e.g. 60-70° C. for heating purposes. The energy factorper 1 kWh used in the heat pump will be around 4 because the coolingaqueous liquid is available at a stable temperature and at a stableflow. These are conditions, which favour the running of a heat pump.

K2: The vapor not condensed in K1 can optionally be diverted to thecondensing device K2, where it is washed in a counter current of aqueousliquid in order to remove a substantial part of the remaining ammonia.The vapor remaining after the washing process can be diverted to avacuum pump and further to a conventional air scrubber or directly tothe atmosphere.

K3: The dilute ammonia/aqueous liquid solution produced in the K1 andoptionally also K2 comprising the first condensed aqueous liquid mediumcomprising ammonia and the aqueous liquid fraction comprising ammonia isstripped for ammonia in the stripper unit K3 by means of hot steam at orabove 100° C. and at a pressure above atmospheric pressure, i.e., at ahigher second pressure (e.g. 2.5 bar) as compared to the lower firstpressure (e.g. 0.16 bar) in S, K1 and optionally also K2.

K4: The concentrated ammonia/steam vapors from the stripper unit K3comprising hot ammonia-comprising steam are condensed in the secondcondensing device K4 by means of cooling aqueous liquid in a coolingtower, preferably to a 25% ammonia/aqueous liquid solution.

B2: The second condensed aqueous liquid medium comprising ammonia andvapor not condensed by the second condensing device from K4 can beseparated in the phase separator B2, and the second condensed aqueousliquid medium comprising ammonia is diverted to a storage tank and thevapor not condensed by the second condensing device is diverted e.g. toan air scrubber or directly to the atmosphere.

K1 and K4: Recycling of heat: The K1 and K4 cooling towers may both besplit in two parts in order for the first part to generate relativelywarm cooling aqueous liquid and in order for the second part to generaterelatively cold cooling aqueous liquid at temperatures less than ambienttemperature. The relatively warm cooling aqueous liquid may in bothcases be used in the shunt or any other heating purpose. The coolingaqueous liquid generated in the first part of K1 will preferably havetemperatures of about 40-45° C. whereas the cooling aqueous liquid fromthe first part of K4 will preferably have temperatures of 70-80° C. Thecooling aqueous liquid from the second part of both K1 and K4 will beless than 25° C.

The cooling-aqueous liquid with temperatures of about 70-80° C. is wellsuited to be recycled to the evaporator E whereas the cooling aqueousliquid with temperatures of 40-45° C. may be used for any other heatingpurpose, e.g. preheating of cold biomass to be introduced into a biogasplant.

FIG. 2 illustrates one embodiment of the shunt and the end-stripperdevice. In this embodiment the shunt and the end-stripper device iscapable of being used with a mobile unit such as a container.

The numbers in the below table refer to reference numerals in thefigure.

Item Indication Description 1 Container 2 S Shunt 3 E Evaporator 4 Pumpbetween E and H6, H5, H3 5 K2 Further condensing device 6 Pump betweenK1 and K2 7 K3 Stripper unit 8 Pump 9 K4 Second condensing device (Heatexchangers H3, H4, H5, H6) 10 K1 First condensing device 11 Coolingtower (not shown) 12 Capsule vacuum blowers 13 Pipe flange 14 Pipeflange 15 Pipe flange 16 Pipe flange 17 Pipe flange 18 Blind flange 19Blind flange 20 Pipe between E and S 21 Manifold between E and S 22Manifold between E and S 23 Manifold between E and S 24 Pipe inletbetween R and S 25 Pipe between K1 and K2 26 Pipe to cooling tower 27Pipe between H2 and H4 28 Pipe between E and pump 6 29 Pipe between E,pump 6 and H6, H3 30 Pipe between E and H6, H3. 31 Pipe between K2 andpump 7 32 Pipe from S to bioreactor R 33 Pipe between S and K1 34 Pipebetween H3 and K3 35 Pipe between H3 and H4 36 Pipe from H4 to anammonia storage tank via a phase separator B2 37 Pipe between pump 7 andK3. 38 Pipe between H6 and external supply of waste heat 39 Pipe forreturn of cooled water between H6 and external heat source 40 Vacuummanifold to K2 41 Water supply to S 42 Exhaust vapor from vacuum blowersto air scrubber

-   -   1. The container wherein the shunt is mounted to provide a        separate unit, which can be integrated with a biochemical        process plant. The container is not shown on the figure, but it        preferably confines all but top of no. 5 and the upper part of        no. 7.    -   2. The shunt S typically operates at a pressure below the        atmospheric pressure. The liquid to be stripped for a part of        its ammonia content is diverted from a bioreactor R to S by        means of a pump or inlet valve. During the passage of the liquid        through S, cold steam is directed through the liquid. The        stripped liquid confining a liquid with a reduced concentration        of ammonia is subsequently pumped back to the bioreactor R.    -   3. Evaporator E. The cold steam for the stripping process is        produced by means of vacuum over a surface of warm aqueous        liquid. This takes place in the evaporator E. The temperature of        the aqueous liquid in the evaporator E is preferably maintained        by means of e.g. cooling aqueous liquid from a motor-generator        unit in a biogas plant, or alternatively, from any other waste        heat source. The waste heat, in the form of warm aqueous liquid,        can be present at temperatures as low as 60-70° C. Aqueous        liquid at higher temperatures may also be used, however, in such        cases the vapor has to be cooled to temperatures suitable to the        microorganisms in the bioreactor. For a biogas reactor        co-digesting animal manures with any other organic biomass the        maximum temperature is 65° C. and the running temperature shall        be close to the operating temperature of the biogas reactor,        i.e. preferably between 55-60° C.    -   4. Pump P6, for pumping liquids and fluids between E and H6, H5,        and H3.    -   5. Further condensing device K2.    -   6. Pump P7, to pump between K1 and K2.    -   7. K3 is a stripper unit for concentrating e.g. ammonia. The        dilute ammonia/aqueous liquid solution produced in the K1 and        optionally also K2 comprising the first condensed aqueous liquid        medium comprising ammonia from K1 and the aqueous liquid phase        comprising ammonia from K2 is stripped for ammonia in K3 by        means of hot steam above 100° C. and at a pressure at or above        atmospheric pressure, i.e., at a higher second pressure (e.g.        2.5 bar) as compared to the lower first pressure (e.g. 0.16 bar)        in S, K1 and K2.    -   8. Pump P8, to pump circulating aqueous liquid for feed of heat        exchanger K1 and K4.    -   9. Heat exchangers H3. H4. H5. H6. The H3 and H4 cool vapor from        K3. The hot ammonia-comprising steam from K3 are condensed in        the heat exchanger condensator H3 and H4 comprising the second        condensing device K4. i.e., the condensation is spilt in two (H3        and H4) so as to re-circulate heat into the evaporator E. In H4        the remaining vapor from H3 are again condensed by means of        cooling aqueous liquid in a cooling tower, to preferably a 25%        ammonia/aqueous liquid solution. H5 cools a liquid from an        external heat source, e.g., from a final stripping step in a        complete biogas and refinement plant. H6 cools liquid from an        external heat source, e.g. from a motor-generator plant fuelled        by biogas from a complete biogas plant.    -   10. First condensing device K1. In the shunt S, where cold steam        is directed through the liquid medium comprising ammonia and        thereby removing a part of its ammonia content, the produced        mixture of steam and ammonia constituting cold        ammonia-comprising steam is diverted from the stripper device S        to the first condensing device K1, where the cold        ammonia-comprising steam is condensed to a dilute        ammonia/aqueous liquid constituting the first condensed aqueous        liquid medium comprising ammonia solution by means of cooling        aqueous liquid in a cooling tower. The vapor not condensed in        the K1 is optionally diverted to the further condensing device        K2 where it is washed in a counter current of aqueous liquid in        order to remove at least part of the remaining ammonia. The        remaining vapor is first diverted to a vacuum pump and further        diverted to a conventional air scrubber or directly to the        atmosphere. Here the CO₂ is also emitted to the atmosphere. This        is important because the final N-fertilizer is free of        bicarbonate and thus a stable product in the form of ammonia        and/or ammonium sulphate.    -   11. The cooling tower, which operates by evaporating aqueous        liquid to the atmosphere thus providing the cooling effect. Not        shown in the figures.    -   12. P1. P2. P3. P4. The capsule vacuum blowers produce the        vacuum.    -   13. Pipe flange.    -   14. Pipe flange.    -   15. Pipe flange.    -   16. Pipe flange.    -   17. Pipe flange.    -   18. Blind flange.    -   19. Blind flange.    -   20. Main pipe connection between the evaporator E and the shunt        S.    -   21. Manifold between the evaporator E and the shunt S.    -   22. Manifold between the evaporator E and the shunt S.    -   23. Manifold between the evaporator E and the shunt S.    -   24. Pipe inlet between the biogas reactor R and the shunt S.    -   25. Pipe connection between the first condensing device K1 and        the further condensing device K2.    -   26. Pipe connection between pump 8 and cooling tower (for        cooling of H2 and H4).    -   27. Pipe connection between H2 and H4.    -   28. Pipe connection between E and pump 6.    -   29. Pipe connection between E, pump 6 and H6, H3.    -   30. Pipe connection between E and H6, H3.    -   31. Pipe connection between K2 and pump 7.    -   32. Pipe connection from S to bioreactor R.    -   33. Pipe connection between S and H2.    -   34. Pipe connection between H3 and K3.    -   35. Pipe connection between H3 and H4.

36. Pipe connection from H4 to an ammonia storage tank via a phaseseparator B2. The second condensed aqueous liquid medium comprisingammonia and vapor not condensed by the second condensing device from K4are separated in a phase separator B2, where the aqueous liquid mediumcomprising ammonia is diverted to a storage tank and the vapor notcondensed by the second condensing device to an air scrubber or directlyto the atmosphere.

-   -   37. Pipe connection between pump 7 and K3.    -   38. Pipe connection between H6 and external supply of waste heat        (warm aqueous liquid at 70-90° C.).    -   39. Pipe connection for return of cooled aqueous liquid between        H6 and external heat source.    -   40. Vacuum manifold to pressurize K2.    -   41. Aqueous liquid supply to the shunt S (for cleaning in place        of S filter elements) and condensing device K2.    -   42. Exhaust vapor from vacuum blowers to air scrubber.

FIG. 3 illustrates yet another embodiment of the stripper device of theinvention. The device comprises a first stripping unit 210 and a secondstripping unit 215, said units being connected by conduits so thatvapor, here about 5% by weight of NH₃ at about 50° C., from the firststripping column 210 is condensed by a first condenser 212. Subsequentlythe condensate and vapor is separated into a condensed phase and a vaporphase at said reduced pressure in a phase separator 213. The condensedphase, here about 5% by weight of NH₃ at about 30-40° C., is pumped tosaid second stripping unit 215 at a reference pressure, here atmosphericpressure (1000 kPa), by means of pump 217. In the second stripping unit,the condensed phase is further stripped to produce a vapor of about 25%by weight of NH₃ at a temperature of about 80° C. in the top of thesecond stripping column. Subsequently this vapor phase is condensed in asecond condenser 216 to a temperature at about 30° C.

The liquid to be treated, here liquid of manure from an organic wastewater treatment plant producing bio gases and treating liquids ofmanure, is let into said first stripping column 210 through a reductionvalve 209 at a temperature of about 60° C.

Said first stripping unit 210 comprises a stripping container 211 forproducing a vapor of volatile components from the liquid at a reducedpressure, here e.g. 200 to 800 hPa below a predetermined referencepressure, here preferably atmospheric pressure. Heat is supplied by aheating means; here a heat exchanger placed at the bottom end of thestripping column 210, which heat exchanger here uses cooling water fromthe biogas production section of organic waste water treatment plant.

Typically said stripping container is a stripping column thecharacteristics of which has been design according to methods known inthe art, including but not limited to designs based on the commercialsoftware design package Hyses™. Typically, it is preferred to usestripping columns having 8-12 theoretical plates. A practicalconstruction of such a stripping column, including design of columnplates, inter-plate conduits, selection of column package materials,etc., is known to a person skilled in the art. Commercial strippingcolumns are generally available from chemical engineering suppliers.

Selecting a proper balance between the energy sources available at theplant site, e.g. either a source of low valued energy such as coolingwater or a high valued energy such as combustion heat or electricity,and the involved temperatures and pressures in generating the vapor andcondensate, a skilled person can provide an optimum design for theapparatus for vapor stripping of volatile components from a liquid, e.g.for generating vapor of said volatile components.

In a preferred embodiment of the apparatus, heat at about 80° C. issupplied to the column at a rate providing a warm vapor of about 5% byweight of NH₃ at a temperature of about 50° C. at the outlet of thecolumn and of a pressure of about 200 kPa.

A residue is taken out of the stripping column, here at the bottomthereof.

A first condenser 212, here a plate type condenser especially suited toresist basic conditions of ammonia which is generally available fromchemical engineering suppliers, is used for condensing said vapor ofvolatile components from said stripping container at said reducedpressure.

A phase separator 213 separates said condensed volatile components andsaid vapor of volatile components from said first condenser 212 into acondensed phase and a vapor phase at said reduced pressure.

At least one vapor evacuation pumps 214, here preferably a displacementpump generally available from chemical engineering suppliers, is usedfor removing dissolved gasses such as carbon dioxide and nitrogen andproducing a reduced pressure below said reference pressure; said vaporevacuation pumps being positioned down stream said first condenser.Vapor gasses are taken out from the vapor phase of the phase separator213 to final scrubbing before being released to the atmosphere (notshown).

Said a second stripping unit 215 comprises a second stripping container215 for producing a vapor of volatile components from said condensedphase at said predetermined reference pressure.

The second stripping container preferably consists of a stripping columnwhich preferably is prepared by same and/or similar methods and means tothose used for making said first stripping column 210, with theexception that considerations be taken for a preferably smaller size ofthe second stripping container column, and for the second strippingcontainer being operated at a higher pressure, e.g. typically operatedat predetermined reference pressure about atmospheric pressure (1000hPa) compared to an operational pressure of about 200 hPa for the firststripping container.

Said second stripping unit further comprises a second condenser 216 forcondensing said vapor of volatile components at said predeterminedreference pressure. This second condenser is preferably prepared by sameand/or similar methods and means to those used for said first condenser212.

A pumps 217, here a centrifuge type pump generally available fromchemical engineering suppliers, is used to pump said condensate fromsaid phase separator 213 to said second stripping column 215.

A residue of the second stripping column, here an aqueous solution ofabout 0.4% by weight of NH₃ at about 98° C., is circulated 218 to theinlet of the first stripping column and there admixed to the inletliquid.

FIG. 4 illustrates the principle of the integration of theshunt/stripper device(s) of the present invention into a plant forprocessing organic material. The plant is described in more detailherein below. In FIG. 4, manure, preferably in the form of a slurry,generated in a house or stable (1) for the rearing of animals, includingdomestic animals, such as pigs, cattle, horses, goats, sheep; and/orpoultry, including chickens, turkeys, ducks, geese, and the like, istransferred to either one or both of a first pretreatment tank (2)and/or a second pretreatment tank (3). Additional organic material notoriginating from an animal house on a farm can also be processed and/orsubjected to pretreatment. Examples include animal and poultrycarcasses, meat and bone meal, and similarly processed products.

The working principles are that the manure, preferably in the form of aslurry including, in one embodiment, water such as reject water used forcleaning the animal house or stable, is diverted to the firstpretreatment tank comprising a stripper tank, where ammonia is strippedby means of addition to the stripper tank of e.g. CaO and/or Ca(OH)₂.However, addition of CaO and/or Ca(OH)₂ to the slurry may also takeplace prior to the entry of the slurry into the first treatment tank orstripper tank.

At the same time as the addition of CaO and/or Ca(OH)₂, or at a laterstage, the pretreatment tank comprising the stripper tank is subjectedto stripping and/or heating, and the stripped N or ammonia is preferablyabsorbed prior to being stored in a separate tank (11). The stripped Nincluding ammonia is preferably absorbed to a column in the strippertank comprised in the first treatment tank before being directed to theseparate tank for storage. As ammonia can also be generated during asubsequent fermentation process, the initial stripping process describedherein above can be combined with the shunt/stripper devices disclosedin the present invention in order to remove ammonia which is notgenerated until fermentation of the optionally pre-treated organicmaterial takes place.

Organic materials difficult to digest by microbial organisms duringanaerobic fermentation are preferably pretreated in a secondpretreatment tank (3) prior to being directed to the first pretreatmenttank (2) comprising the stripper tank as described herein above. Suchorganic materials typically comprise significant amounts of e.g.cellulose and/or hemicellulose and/or lignin, e.g. preferably more than50% (w/w) cellulose and/or hemicellulose and/or lignin per dry weightorganic material, such as straws, crops, including corn, crop wastes,and other solid, organic materials. N including ammonia is subsequentlystripped from the pretreated organic material.

In both the first and the second pretreatment tank, the slurry issubjected to a thermal and alkali hydrolysis. However, the temperatureand/or the pressure is significantly higher in the second pretreatmenttank, which is therefore preferably designed as a closed system capableof sustaining high pressures.

The slurry having optionally been subjected to a pre-treatment asdescribed herein above is preferably diverted to at least onethermophile reactor (6) and/or at least one mesophile biogas reactor(6). The slurry is subsequently digested anaerobically in the reactorsconcomitantly with the production of biogas, i.e. gas consisting ofmainly methane optionally comprising a smaller fraction of carbondioxide. The biogas reactor(s) preferably forms part of an energy plantfor improved production of energy from the organic material substrate.

The shunt/stripper devices disclosed herein can be operationally coupledto any of the above at least one thermophile reactor (6) and/or at leastone mesophile biogas reactor (6). The shunt can further be connected toa pre-shunt degassing unit as disclosed herein. The coupling of theshunt/stripper device(s) to the fermentor(s) can be a permanentcoupling, i.e. a fixed system, or it can be a transient couplinginvolving a mobile unit comprising the shunt/stripper device(s).

The biogas can be diverted to a gas engine, and the energy generatedfrom this engine can be used to heat the stripper tank or used to heat aheating source which can be diverted to the evaporator as disclosedherein, where the heating source is subjected to a reduced pressure,said lowering of the pressure generating cold steam. However, the biogascan also be diverted into a commercial biogas pipeline system supplyinghousehold and industrial customers.

The remains from the anaerobic fermentation, still in the form of aslurry comprising solids and liquids, is in a preferred embodimentdiverted to at least decanter centrifuge (7) for separating solids andfluids. One result of this separation is an at least semi-solid fractioncomprising almost exclusively P (phosphor), such as an at leastsemi-solid fraction preferably comprising more than 50% (w/w) P (12). Inthe same step (7), or in another decanter centrifuge separation step(8), a liquid fraction preferably comprising almost exclusively K(potassium), such as at least 50% (w/w) K (13) is preferably alsoobtained. These fractions, preferably in the form of granulates obtainedafter a drying step, including a spray drying step or a slurry dryingstep, preferably comprise P and/or K in commercially acceptable puritiesreadily usable for commercial fertilisers (10). Such fertilisers may bespread onto crops or agricultural fields. The liquids (9) also resultingfrom the decanter centrifuge separation step, such as reject water, canalso be diverted to agricultural fields, they can be diverted back tothe stable or animal house, or into a sewage treatment system.

In another embodiment, only phosphor (P) is collected following decantercentrifuge separation, and water in the form of reject water iscollected in a separate tank for further purification, including furtherremoval of N, removal of odours, and the majority of the remainingsolids. This may be done e.g. by aerobic fermentation. Potassium (K) canalso be separated from the liquids at this stage.

In a further preferred embodiment, the first pretreatment tank canoptionally be supplied with organic material originating from silagestores (4) comprising fermentable organic materials. The divertion ofsuch organic materials to the first pretreatment tank may comprise astep involving an anerobic fermentation such as e.g. thermophilicfermentation tank capable of removing gasses from the silage.Additionally, straws and e.g. crop wastes originating from agriculturalfields (5) may also be diverted to stables or animal houses and later tothe first and/or second pretreatment tank.

FIGS. 5 & 6 disclose in combination another example of a plant forprocessing organic material with which the shunt/stripper device(s) ofthe present invention can be integrated. The different parts of theplant is disclosed herein below in more detail.

Animal Houses

The animal houses (Component number 1) serves to provide an optimal foodsafety and food quality, an optimal animal welfare and workingconditions for the labour personal in the housings, an optimal slurrymanagement, suitable for processing as disclosed herein, and a reductionof emissions to the external environment to a minimum (ammonia, dust,odour, methane, dinitrogen oxide and other gasses).

The housing system can consist of one or more early weaning houses witha total of e.g. 10 sections designed to produce about 250 livestockunits annually. Each section houses e.g. 640 piglets (7-30 kg) or 320slaughter pigs (30-98 kg).

An amount of about 10.000 m3 slurry can be expected to be producedannually from such animal houses. In addition to this volume an amountof 5-10.000 m3 process water shall be recycled through the houses.

Slurry Collection Tank

The function of a slurry collection tank (Component number 2) is tocollect slurry form the daily flushings of the animal houses and to workas a buffer before pumping to the main reception tank. The slurry isdiverted to the collection tank by means of gravitation. The volume ofthe tank can be anything appropriate, such as e.g. about 50 m³. The tankcan be made of concrete and it can be placed below the floor in theanimal houses so that the slurry form the houses can be diverted to thecollection tank be means of gravitation.

Main Reception Tank

Slurry from the collection tank is preferably pumped to the mainreception tank (Component number 3). Other types of liquid manure/waste,such as e.g. meat and bone meal, can also be added to the reception tankfrom other farms/processing plants. Besides meat and bone meal, minkslurry, cattle slurry, molasses, vinasses, silage etc. can be added tothe main reception tank. The material can transported to the receptiontank by lorry and can be loaded directly into the reception tank. Thevolume/capacity is anything appropriate, such as e.g. about 1.000 m³.The level in the stripper and sanitation tank (12, see below) preferablycontrols a pump, which pumps slurry from the reception tank to thestripper and sanitation tank. The dose adjustment can be manual orautomatic. The maximum capacity can be anything appropriate under thecircumstances.

CaO Addition

When slurry is being pumped from the reception tank 3 to the stripperand sanitation tank 12, lime is added to the slurry in order to increasethe pH. The lime addition manifold is preferably adjusted to add 30-60 gCaO/kg (dry weight). The lime is preferably supplied as a powder whichcan be blown into the silo from the lorry. The volume/capacity of thesilo can be e.g. about 50-75 m³. The dose of 30-60 g/kg (dry weight)corresponds to app. 6-12 kg CaO per hour with a slurry capacity of 3.5m³/h with 6% (dry weight).

When added directly to the slurry (6% dry weight), the lime dose isabout 60 g/kg (dry weight) yield (about 8.8 kg CaO per hour). It ishowever preferred to add the lime directly to the alkali pressuresterilazation and hydrolysis unit. When lime is added directly to thepressure unit (the E-media hold 20-70% (dry weight)), the lime dose isabout 30-60 g/kg (dry weight). 60 g/kg (dry weight) equals about 342 kgCaO per batch, while 30 g/kg d.m. equals about 171 kg CaO per batch.

Balance Installation

An optional balance (Component number 5) can weigh the incoming E-media(energy containing organic material). The suppliers will preferablyspecify the type of media which is supplied to the plant, i.e. deeplitter, energy crops etc. of various sorts.

The specification shall be made by selecting the relevant E-media on acontrol panel. According to the suppliers panel registration, the weightof received E-media incl. specification of media can be recorded.

Reception Station for Deep Litter and Energy Crops

An optional reception station (Component number 6) shall receive deeplitter from e.g. poultry or other animals as well as energy crops. Thestation is preferably a large silo equipped with several screw conveyorsin the floor. The lorries will empty their load of E-media directly intothe silo. The volume/capacity can be anything appropriate under thecircumstances, such as e.g. a yearly capacity of E-media (about 51.5%(dry weight)) of about 9.800 tonnes. The volume of the silo can be fromseveral cubic meters to about 100 m³, corresponding to three dayscapacity (65 hrs). The materials are preferably concrete/steel.

The reception station is connected to the lime pressure cooker via atransport and homogenization system.

Silo for Energy Crops

An optional silo for energy crops (Component number 7) serves to providestorage means for energy crops. The crops are preferably conserved assilage. The volume/capacity can be e.g. from about 5.000-10.000 m³. Thesilo can be a closed compartment from which silage juice is collectedand pumped to the reception tank. The silage can be degassed and/orfermented before being diverted to the reception station.

Transport- and Homogenisation System for Deep Litter and Energy Crops

A transport- and homogenisation system (Component number 8) for deeplitter and energy crops preferably receives E-media from the screwconveyors in the floor of the reception station. The E-media can betransported by additional screw conveyors to the cooking units and atthe same time preferably macerated by an integrated macerator. Thevolume/capacity can be anything required under the circumstancesincluding about 1.5 m3 E-media/hour, or 8.200 tonnes of E-media/year.The capacity of the transport- homogenisation system is preferably notless than about 30 m3/hour. Three fundamental parameters shall controlthe addition of E-media, i.e. volume, weight per volume, and time. Fromthese parameters volume per unit time, time and thus total volume andweight shall be established.

Alkali Pressure Sterilization and Hydrolysis Unit

An alkali pressure sterilization and hydrolysis unit, such as a limepressure cooker, (Component number 9) shall serve two main purposes,i.e. firstly elimination of microbial pathogens in the E-media inparticular in deep litter from various poultry or other animalproductions and secondly, at the same time hydrolyse structuralcomponents of the litter in order to render them available for microbialdegradation in the fermentors.

The unit shall also preferably eliminate or at least substantiallyreduce any vira and/or BSE-prions if present in waste introduced intothe plant. Such waste include meat- and bone meal, animal fats orsimilar produce from the processing of animals not used for consumption.In this way it is envisaged that e.g. meat and bone meal originatingfrom cattle potentially infected with BSE can be used in accordance withthe present invention. Similarly, poultry having contracted diseasessudh as e.g. Newcastle disease can also be used.

Filling of the pressure sterilizer is provided by the transport- andhomogenisation system, which transports E-media into the according totype of E-media as defined on the balance installation.

The alkali pressure sterilization and hydrolysis unit generates a numberof different 30 gasses and other undesirable odourants. Examplesinclude:

-   -   Carboxylic acids    -   Alcohols    -   Phenolics    -   Aldehydes    -   Esters    -   Nitrogen heterocycles    -   Amines    -   Sulphides    -   Thiols (mercaptans)

The above compounds are either acidic, basic or neutral. Accordingly,the absorption column preferably comprises three columns in order totake account of the different chemistries needed in order to neutralizethese compounds.

The gas phase generated in the alkali pressure sterilization andhydrolysis unit is initially diverted to an absorber complex comprisingi) base-absorber capable of removing acidic components, then the gasphase is diverted to ii) an acid absorber capable of removing basiccomponents such as e.g. ammonia and amines, and finally the gas phase isdiverted to iii) a hypochlorite absorber capable of oxidizing theneutral compounds.

The alkali pressure sterilization and hydrolysis unit preferablycomprises an elongated chamber with inlet(s) and outlet(s) port(s) forthe organic material. A stirrer is located in the center of theelongated chamber. Hot vapor/steam is used for heating the organicmaterial. The steam can be entered directly into the chamber.

Solid organic material can be diverted to the alkali pressuresterilization and hydrolysis unit via a valve. Liquid organic materialcan be diverted to the alkali pressure sterilization and hydrolysis unitvia a nozzle or a connecting piece. The alkali pressure sterilizationand hydrolysis unit also comprises an outlet for diversion of gasseoussubstances to the absorber complex described herein elsewhere.

The operating parameters are as follows:

Pressure: 2-10 bar Temperature: 100-220° C. Processing time: Preferablyless than 2 timer (about 40 min. at 160° C.)

After processing in the alkali pressure sterilization and hydrolysisunit, the pressure can be lowered by diversion of cold biomass ororganic material to the alkali pressure sterilization and hydrolysisunit. The processed organic material is preferably removed from thealkali pressure sterilization and hydrolysis unit while still under somepressure.

Mixing Tank for Pressure-sterilized E-media and Raw Slurry

Following sterilization and hydrolysis in the pressure unit, the treatedbiomass is allowed to expand into a mixing tank (Component number 10)preferably located below the pressure unit. Excess pressure (steam) isreleased into the stripper and sanitation tank in order to collectammonia and transfer heat to the stripper tank biomass before expansioninto the mixer tank.

The purpose of the mixer tank is to mix cold raw slurry from thereception tank with hot sterilized E-media in order to obtain heattransfer (re-use of heat) and mixing of the two media.

The volume/capacity is e.g. about 25 m³. Any suitable material can beused, including insulated glasfibre. The working temperature istypically about 70-95° C.

Tank for Liquid Biomass

The liquid biomass contained in the tank for liquid biomass (Componentnumber 11) can be used to ensure sufficient biogasproduction during thestart up phase of the whole plant. However, it can also be usedoccasionally, when such liquid biomass is available. Liquid biomassinclude e.g. fish oil, and animal or vegetable fats. Vinasses andmolasses can also be used, but this is not preferred because of therelatively high water content and thus low potential energy content perkg product.

The volume/capacity is typically about 50 m³, and a suitable materialfor the tank is stainless steel. The contents of the tank is preferablyliquids and solids having a particle size of max. 5 mm. Stirring as wellas a heating system for temperature control is preferably provided, asare feeding pump(s) to the fermentor(s). The temperature shallpreferably be min. 75° C. so that oily or fatty biomass can be pumpedinto the fermentor(s).

Stripper and Sanitation Tank

The stripper and sanitation tank (Component number 12) preferablyreceives the following media:

-   -   Slurry from reception tank (3) and/or    -   E-media from the pressure cooker (9), and/or    -   Possibly liquid biomass from biomass liquid tank (11), and/or    -   Reject water from decanter (18) or possibly after K-separation        (25).

The purpose of the tank is to regenerate heat used in the pressurecooker by heating the slurry from the reception tank, to mix the E-mediawith slurry and hence to produce a homogeneous feed to the fermentors,to control pH before feeding to fermentors, and to sanitise the slurry.

The stripper and sanitation tank strips ammonia, and ammonia fluid isdiverted to an absorption column. Microbial pathogens are eliminated andthe media/slurry is prepared for anaerobic digestion.

The stripper and sanitation tank supplies the fermentor(s) withpre-treated material for fermentation. In a timed process the materialwill be transported to the fermentors. The demand of material depends onthe digestion process in the fermentors. One, two, three or morefermentors can be employed.

The stripper and sanitation tank is regularly filled with slurry andE-media from the alkali pressure process. Finally, to obtain a drymatter of about 15% (dry weight) one or more level switches regulate thecontent in the tank. A (dry weight)-mesuring unit regulates the contentof (dry weight). Every e.g. 1 hour after filling of slurry and E-mediait is possible to pump E-media to the fermentor(s).

The top of the stripper and sanitation tank is preferably ventilatedthrough an ammonia-absorbing unit, and a pH-measuring unit regulates theneed for CaO. A timed process can optionally pump water/slurry into thedrizzle system to prevent production of foam.

Fermentors for Biogas Production

Digestion of the biomass is provided by a multi-step fermentor systempreferably comprising three fermentors (Components 13, 14 and 15).Systems with fewer as well as more fermentors can also be applied.

The fermentors are preferably connected to achieve maximum flexibilityand optimum biogas production. The fermentors shall be planned forroutinely running at termofile (45-65° C.) as well as mesofile (25-45°C.) temperatures, respectively. Regulation of pH is possible throughaddition of an organic acid (liquid) in necessary quantities.

The fermentors preferably receives the following media:

-   -   E-media from the stripper and sanitation tank (12)    -   Liquid biomass from the liquid biomass tank (11)    -   Acids from the acid tank (16)

The running conditions can be any conditions suitable, including

Media: All sorts off animal manure, primarily pigs slurry. Maceratedenergy crops. Some sorts of organic waste, CaO, organic Acids Runningtemperature: 35-65° C. Running gas combination: 65% CH₄, 33% CO₂, 2%other gases Insulation k-value: 0.25 W/m²K heatloss is estimated to 10kW Running Max. Pressure: +20 mbar abs. (No vacuum) Max. viscosity inmedia: 12% (dry weight) Base/Acid-range: 5-10 pH Abrasive rudiments inmedia 1-2% (Ex. Sand): Max. temperature in heating 80 degrees celciuselements: Max. effects in heating elements: 600 kW Transmission effect: 7.5 kW/20-25 rpm

The digestion shall preferably be run at from about 55° C. to about 65°C., such as at about 60° C. as disclosed herein in more detailelsewhere. Heat loss is estimated to about 10 kW. The biomass in thetank is can be heated from 5° C. to 55° C. during 14 days, with thepossibility of addition of acid for adjustment of pH.

The shunt/stripper device(s) as disclosed in detail herein elsewhere ispreferably operationally linked to the above fermentor(s) in order toremove ammonia and thereby preventing any undesirable excess of ammoniain the fermentors. A “pre-shunt” degasser can optionally be included asdescribed herein elsewhere.

The generated biogas can e.g. be diverted to a gas engine/motor capableof heating a heating source which can subsequently be diverted to theevaporator. Following a lowering of the pressure cold steam isgenerated. The cold steam is diverted to the shunt for stripping offammonia and optionally also other volatile compounds.

Tank for Organic Acids for pH Adjustments in Fermentors

A tank for organic acids (Component number 16) for pH adjustments in thefermentor(s) is preferably also provided.

Buffer Tank for Degassed Slurry before Decanter

Following digestion of the biomass in the fermentors the degassedbiomass is optionally pumped to a buffer tank (Component number 17)before being subjected to separation in the decanter. The biomass canalso be diverted directly to a decanter installation as described below.

Decanter Installation

The function of the decanter installation (Component number 18) is toextract suspended solids (ss) and P from the biomass.

The decanter separates the digested biomasse into the two fractions i)solids, including P, and ii) reject water.

The solids fraction contains 25-35% d.m. App. 90% of the ss. and 65-80%of the P-content of the digested biomass is extracted. In case ofaddition of PAX (Kemira Danmark) to the buffer tank before separation inthe decanter, app. 95-99% of the P can be extracted. The solids fractionis transported to containers by means of a shaft less screw conveyor.

The rejectwater contains 0-1% ss and dissolved K. The ss depends on theaddition of PAX. The principal component of the reject waters isdissolved K which amounts to app. 90% of the original K-content in thebiomass. The reject water is pumped to the reject water tank.

P-fraction Transport System and Treatment

From the decanter installation the solid matter fraction (routinelycalled the P-fraction) can be transported to a series of containers bymeans of conveyor screws and belts forming a P-fraction transport system(Component number 19).

A common conveyor band transports P-fraction to a storage where it isstacked into miles, covered with a compost sheet and allowed to compost.The composting process further dries the P-fraction and the d.m.-contentthus increases to 50-60%.

Second N-stripping Step

Efficient stripping of ammonia from the reject water is preferred, and aresidual level of about 10 mg NH₄—N/ltr or less is preferred.

The second stripping step can be carried out be using a steam stripperoperated at ambient pressure. Examples of preferred steam strippers aredisclosed herein elsewhere.

The stripper principle benefits form the different boiling temperaturesof ammonia and water. At temperatures close to 100° C. extraction ofammonia is most efficient.

The use of energy in order to heat the feed is an essential runningparameter. The stripper unit shall therefore preheat the feed beforeentering the stripper column to close to 100° C. This can be provided byusing steam (or possibly warm water and steam) from a motor generatorunit in a steam-water heat exchanger.

When heated the feed enters the stripper column and percolates over thecolumn while at the same time being heated to the running temperature bya counter current of free steam. The steam/ammonia gas is subsequentlycondensed in a one or two step condensator. From the floor of the columnthe water now essentially free of ammonia is pumped to a levelcontrolled exit pump.

The stripped ammonia can be diverted to the bottom of a two-stepscrubber condensator where the ammonia gas is condensed primarily in acounter current of cooled ammonia condensate. The ammonia gas notcondensed can optionally be condensed in a counter current of pure water(possibly permeate from the final reverse osmosis step). If the use ofacid is desirable or necessary it is appropriate to use sulphuric acidat this stage. It is thus possible to achieve a higher finalconcentration of ammonia. The scrubber condensator is preferablyconstructed from a polymer in order to allow the use of acids.

The second end-stripping strip is preferably carried out by using thestripper device described herein above (i.e. without the device beingconnected to the shunt, but instead).

Ammonia Absorption Column (for use with First and/or Second N-stripping)

In one embodiment, a condensate scrubber can be used in order to gainflexibility concerning addition of acid. The column (Component number21) is preferably constructed in two sections so that the fraction ofammonia not condensed in the first section is subsequently condensed inthe second section. This takes place in a full counter current so thataddition of water is limited as much as possible. Thereby a maximumammonia concentration in the final condensate is reached (about or morethan 25%). The ammonia product can be pumped out with a separate pump orbe taken out from a valve on the circulation pump. The absorption may beassisted by addition of sulfuric acid into the water counter current.

The ammonia absorption column is preferably an acid absorber, and thecolumn forms part of an absorber complex comprising i) base-absorbercapable of removing acidic components, ii) an acid absorber capable ofremoving basic components such as e.g. ammonia and amines, and iii) ahypochlorite absorber capable of oxidizing the neutral compounds.

Sulphuric Acid Tank

The sulphuric acid tank is used for storing the sulfuric acid used inthe N-stripping process. (Component number 22).

NS Tank

The NS tank (Component number 23) is used for storing the stripped N.

Gas Store

It is preferred to establish a gas store (Component number 24) as abufferstore for the feeding of e.g. a motorgenerator engine.

Rejectwater Tank

From the decanter installation the rejectwater is preferably pumped tothe rejectwater tank (Component number 25).

The rejectwater tank is equipped with a submerged micro-filter withstatic operation. The micro-filter shall remove particles larger than0.01-0,1 μm. A negative pressure of 0.2-0.6 bar can be built up at themembrane. Hence the permeate is sucked through the membrane retainingthe particles on the membrane surface. In order to prevent membranefouling and scaling the coating of the membrane surfaces has to beremoved by a periodic backwash procedure.

A micro-processor control device shall automatically control theextraction of permeate and the backwash procedure. The extraction shallbe interrupted by periodic backwash e.g. for 35 seconds for every 300seconds running time. The total flow shall be 2-6 m3 per hr.

Aeration may be applied to assist the micro-filtration. Aeration imposeshear stress on the membrane surface reducing scaling and fouling. Itfurther aerates the reject-water and stimulates aerobic decomposition ofresidual organic matter, nitrification and denitrification. Possibleremaining odour, nitrate etc. is thus removed during the process ofmicro-filtration.

From this tank the permeate shall be used for:

-   -   Rinsing of the animal houses, canals, slats etc.    -   Further separation. Dissolved K shall be concentrated by means        of reverse osmosis, the K-fraction being stored in a separate        storage tank. Water for rinsing animals houses may also be taken        form this permeate flow.    -   The K may also be concentrated through other means such as        mechanical or steam compression. This depends on the specific        choice for each specific plant and amount of excess heat        available for steam compression.

The reject water tank containing the concentrate from themicro-filtration shall be emptied at regular intervals to remove theparticle concentrate. This shall be added to either the K-fraction orthe P-fraction from the decanter.

K tank

The K tank (component number 26) serves the purpose of storing thepotassium (K) concentrate.

Gas Cleaning

The biogas produced in the fermentors may contain trace amounts ofhydrogen sulfide (H₂S) which are necessary to remove (Component number27) before burning the biogas in a combined heat and power plant.

The gas shall be cleaned by employing the ability of certain aerobicbacteria to oxidise H₂S into sulfate. The genus shall primarily be thegenus Thiobacillus which is known form several terrestrial and marineenvironments. Other genus may also be used such as Thimicrospira andSulfolobus.

A tank made of glass fiber packed with plastic tubes with a largesurface area shall be rinsed with reject water to maintain the packingmaterial moist. The biogas is diverted through the packed column and anair stream (of atmospheric air) is added to the biogas stream. Theatmospheric air is added to provide an oxygen concentration of 0.2% inthe gas stream, i.e. sufficient to oxidize the H₂S and therefore not toproduce an explosive mixture of biogas and oxygen. A ring side blower isused.

Combined Heat and Power plant (CHP)

The main component in the CHP (Component number 28) can be e.g. a gasfired engine connected to a generator for production of electric power.The main priority for the CHP is to produce as much electric power aspossible relatively to heat. The engine is preferably cooled by a watercircuit (90° C.) and the generated heat is preferably used in the plantprocess and/or to the heating of e.g. the animal houses.

The exhaust gas is used in a recuperator for steam production. The steamis used as heating source in the plant process, i.e. in the pressuresterilization unit and in the n-stripper. Depending on the amount ofsteam it may also be used for concentrating the K in the rejectwater(seam evaporation).

The generated heating source is also capable of being diverted to theevaporator operationally linked to the shunt. A lowering of the pressurein the evaporator results in the generation of cold steam which can bediverted to the fermentation liquid contained in the shunt. Volatilecompounds such as e.g. ammonia can be stripped at least partly from thefermentation liquid in this way as described herein elsewhere, and theat least partly stripped fermentation liquid in the shunt can bereturned to the fermentor.

Between the steam and heat circuit, there will be installed a heatexchanger, so it is possible to transfer heat from the steam system tothe heat system. In addition to the above mentioned genset there will beinstalled a steam boiler. This boiler will be used for heat productionto start the process, and in addition be used as a backup for thegenset. If there is produced more steam than needed in the plantprocess, the rest production can be flashed of in a cooler.

To start the plant process (heating of fermentor tanks) etc., heat isprovided by e.g. an oil fired boiler. As soon as gas production isachieved the oil burner will be switched to a gas burner. As soon as gasproduction is large enough to start the engine, the engine will takeover the heat production.

Potassium Separation

At least two alternatives for separating potassium from the rejectwaterare possible (Component number 29). At relatively high levels of biogasproduction the motor-generator engine produces excess heat (steam at160° C.) which can be used to concentrate the K. The distillate free ofnutrients may be used for field irrigation or recycled through the wholeplant.

At relatively low rates of biogasproduction a micro-filter can be usedto filter particles larger than 0.001 μm, such as larger than 0.01 μm,for example larger than 0.1 μm from the reject water rendering thepermeate suitable for treatment in a standard reverse osmosis filter.The K shall preferably be concentrated to a 5-15% (v/v) solution,optionally a 10-20% (v/v) solution.

1. A system comprising a stripper device for stripping volatilecompounds from a liquid medium, said stripper device comprising: a) ashunt to which aqueous liquid medium comprising volatile compounds canbe diverted in the form of a side stream to at least one fermentorand/or at least one biogas reactor, b) means for diverting aqueousliquid medium comprising volatile compounds to the shunt from said atleast one fermentor and/or at least one biogas reactor, c) an evaporatordevice comprising a sample of aqueous liquid to which heat obtained froman external heat source can be added, wherein a reduction of thepressure in said evaporator to a first pressure below a predeterminedreference pressure generates cold steam, d) means for directing the coldsteam generated by the evaporator of c) through said aqueous liquidmedium comprising volatile compounds in the shunt of the stripper deviceat said pressure below a predetermined reference pressure, therebystripping off volatile compounds and obtaining a cold, volatilecompound-comprising steam, e) a first condensing device, f) means fordiverting said cold volatile compound-comprising steam at said pressurebelow the predetermined reference pressure to the first condensingdevice, and condensing in a first condensing step in said firstcondensing device said cold volatile compound-comprising steam at saidpressure below a predetermined reference pressure, thereby obtaining afirst condensed aqueous liquid medium comprising said volatile compoundsand vapor not condensed by the first condensing device, g) a stripperunit for stripping volatile compounds at said predetermined referencepressure or at a second pressure higher than said predeterminedreference pressure, h) means for diverting said first condensed aqueousliquid medium comprising volatile compounds obtained in f) to thestripper unit, and stripping off at least part of the volatile compoundsfrom said first condensed aqueous liquid medium comprising volatilecompounds by injecting hot aqueous steam at said reference pressure orat the higher second pressure, thereby obtaining a hot volatilecompound-comprising steam and aqueous liquid stripped off at least partof said volatile compounds, i) a second condensing device, and j) meansfor diverting said hot volatile compound-comprising steam to a secondcondensing device, and condensing said hot volatile compound-comprisingsteam, thereby obtaining a condensate comprising volatile compounds. 2.The system according to claim 1, wherein the stripper device furthercomprises a further condensing device and means for diverting said vapornot condensed by the first condensing device to the further condensingdevice for removing at least some of the remaining volatile compoundsfrom said vapor not condensed by the first condensing device, saidfurther condensation involving the step of washing the vapor in acounter current of aqueous liquid, thereby obtaining a combined aqueousliquid fraction comprising the first condensed aqueous liquid mediumfrom the first condensing device and volatile compounds condensed in thefurther condensing device, and optionally vapor not condensed by thefurther condensing device.
 3. The system according to claim 2 furthercomprising means for diverting said combined aqueous liquid fraction tothe stripper unit.
 4. The system according to claim 2, wherein thestripping of volatile compounds in the stripper unit results in theformation of a stripped aqueous liquid medium comprising at the most 200ppm volatile compounds.
 5. The system according to claim 4, wherein saidsecond condensing device comprises two heat exchangers for cooling saidhot volatile compound-comprising steam in two steps, said coolinggenerating said condensate comprising volatile compounds in two steps,said second condensing device further generating a heating source, saidsystem further comprising means for directing said heating source tosaid evaporator for heating aqueous liquid in said evaporator.
 6. Thesystem according to claim 1 further comprising means for divertingaqueous liquid medium stripped for essentially all of said volatilecompounds from said stripper unit to said shunt.
 7. The system accordingto claim 1 wherein the shunt further comprises a pre-degassing unit forremoving at least one undesirable gas affecting ammonia stripping fromthe organic material before the remaining part of the organic materialis contacted by the cold steam generated by the evaporator.
 8. Thesystem according to claim 7 wherein each undesirable gas is selectedfrom the group consisting of methane, carbon dioxide and hydrogendisulphide.
 9. The system according to claim 1, wherein said referencepressure is 1 bar.
 10. The system according to claim 9, wherein thefirst pressure is from about 0.05 to about 0.4 bar.
 11. The systemaccording to claim 9, wherein the second pressure is from about 2 to 3bar.
 12. The system according to claim 9, wherein the first pressure isfrom about 0.1 to 0.2 bar.
 13. The system according to claim 9, saidsystem further comprising at least one air scrubber for cleaning saidvapor not condensed by the first condensing device and/or said vapor notcondensed by the second condensing device.
 14. A mobile unit comprisingthe system according to claim 1, wherein said mobile unit can beconnected to a fixed installation in the form of at least one fermentorand/or at least one biogas reactor.
 15. A plant for processing organicmaterial comprising solid and liquid parts, said plant comprising thesystem according to claim 1, said plant further comprising at least onefermentor and/or at least one biogas reactor, wherein said organicmaterial is fermented at mesophilic and/or thermophilic conditions. 16.The plant according to claim 15, said system further comprising astripper tank for stripping nitrogenous compounds from the organicmaterial prior to fermentation or biogas production.
 17. The plantaccording to claim 15, said system comprising a pre-treatment tank forhydrolysing organic material prior to an initial stripping ofnitrogenous compounds from the organic material and/or prior tofermentation and/or biogas production of the organic material.
 18. Theplant according to claim 15, said system further comprising a limepressure cooker for hydrolysing organic material.
 19. The plantaccording to claim 15, said system further comprising at least onesilage storage tank for generating ensiled plant material.
 20. The plantaccording to claim 19, said system further comprising a pre-treatmentfermenting tank for fermenting silage and/or lime pressure cookedorganic material, in which the fermentation conditions are selected frommesophilic fermentation conditions and/or thermophilic fermentationconditions.
 21. The processing plant according to claim 15 comprising i)a lime pressure cooker for hydrolysing the organic material, ii) astripper tank for stripping ammonia from said lime pressure cookedorganic material, and wherein said at least one fermentor and/or atleast one biogas reactor is for fermenting said lime pressure cooked andammonia stripped organic material.
 22. The plant according to claim 21,said system further comprising a reception station for receiving organicmaterial comprising solid parts and a transport and homogenisationsystem for homogenizing organic material comprising solid parts andtransporting the homogenized organic material comprising solid parts tothe lime pressure cooker.
 23. The plant according to claim 22, whereinthe transport and homogenisation system comprises screw conveyors and anintegrated macerator.
 24. The plant according to claim 22, wherein thereception station is fitted with screw conveyors in the floor of thereception section, and wherein the transport and homogenisation systemcan receive the organic material comprising solid parts from the screwconveyors located in the floor of the reception station.
 25. The plantaccording to claim 22, wherein the lime pressure cooker is alsoconnected to a reception tank for receiving liquid organic material,wherein liquid organic material can be diverted from said reception tankto said lime pressure cooker.
 26. The plant according to claim 21,wherein the lime pressure cooker comprises a single chamber and astirrer, an entry port for entering organic material to be lime pressurecooked, and an outlet for diverting the lime pressure cooked organicmaterial to a mixing tank or to said at least one fermentor and/or atleast one biogas reactor connected to said system.
 27. The plantaccording to claim 26, wherein a container for lime addition isconnected to the lime pressure cooker, and wherein the mixing tankconnected to the lime pressure cooker is also connected to a receptiontank for receiving organic slurries, wherein the mixing tank is used formixing lime pressure cooked organic material with organic slurriesdiverted to the mixing tank from a reception tank.
 28. The plantaccording to claim 27, wherein the container for lime addition comprisesa by-pass for adding lime directly into the mixing tank.
 29. The plantaccording to claim 27, wherein the mixing tank is connected to thestripper tank so that the mixture of the lime pressure cooked organicmaterial and the organic slurries from the reception tank can be pumpedinto the stripper tank.
 30. The plant according to claim 29, wherein thestripper tank is further connected to the reception tank in order toreceive organic slurries from the reception tank and also connected tothe lime pressure cooker in order to receive lime pressure cookedorganic material from the lime pressure cooker.
 31. The plant accordingto claim 26, wherein the mixing tank and the stripper tank are connectedby a macerator for macerating lime pressure cooked organic material andorganic slurries to be diverted from the mixing tank to the strippertank.
 32. The plant according to claim 26, wherein the stripper tank isconnected to an absorption system comprising a base absorber forabsorbing acidic compounds, an acid absorber for adsorbing basiccompounds, and a hypochlorite oxidizer for oxidizing neutral compounds.33. The plant according to claim 32, wherein the acid absorber absorbsammonia stripped from the stripper tank.
 34. The plant according toclaim 33, wherein the absorption system is connected to a sulphuric acidtank and to a tank for storing a final ammonia condensate.
 35. The plantaccording to claim 32, wherein the lime pressure cooker is alsoconnected to the absorption system, and wherein any ammonia strippedfrom the lime pressure cooked organic material is also diverted to theabsorption system.
 36. The plant according to claim 21, wherein theplant further comprises an animal housing system connected to acollection tank for collection of organic slurries produced by theanimals in the animal housing system, wherein the collection tank isconnected by a pump to a reception tank for receiving organic slurriesso that organic slurries can be pumped from the collection tank to areception tank.
 37. The plant according to claim 36, wherein thecollection tank is located below the floor of the animal housing systemso that organic slurries can be diverted to the collection tank by meansof gravitation.
 38. The plant according to claim 21, wherein the systemfurther comprises a pre-treatment fermentation tank for fermenting limepressure cooked organic material before the lime pressure cooked organicmaterial is subjected to a second ammonia stripping step in the strippertank for stripping ammonia from said lime pressure cooked and fermentedorganic material.
 39. The plant according to claim 38, wherein thestripper tank and/or the lime pressure cooker is connected to a silagestore comprising a fermentable organic material.
 40. The plant accordingto claim 39 further comprising an anerobic pre-treatment fermentationtank capable of removing gasses or odourants from silaged organicmaterial and/or lime pressure cooked organic material, and wherein thesilaged organic material and/or the lime pressure cooked organicmaterial can be diverted to the anaerobic fermentation tank before beingsubsequently diverted to the stripper tank.
 41. The plant according toclaim 40, wherein the anaerobic pre-treatment fermentation tank is athermophilic fermentation tank.
 42. The plant according to claim 40,wherein the anaerobic pre-treatment fermentation tank is a mesophilicfermentation tank.
 43. The plant according to claim 21, wherein theplant further comprises a pre-treatment fermentation tank for fermentingorganic material before the organic material is subjected to limepressure cooking and ammonia stripping.
 44. The plant according to claim21, wherein the stripper tank is connected to at least one fermentorand/or at least one biogas reactor connected to said system.
 45. Theplant according to claim 44, wherein the at least one biogas producingfermentor is connected to a tank for collection of biogas.
 46. The plantaccording to claim 45, wherein the plant further comprises an outlet fordiverting the biogas into a commercial biogas pipeline system.
 47. Theplant according to claim 44 further comprising a gas cleaning unit forremoving hydrogen sulphide and other odourants present in the producedbiogas.
 48. The plant according to claim 44 further comprising a gasfired engine connected to a generator for production of electric powerand heat.
 49. The plant according to claim 48, wherein the plantcomprises pumps, valves and pipes allowing use of the energy generatedby the gas fired engine for heating the stripper tank.
 50. The plantaccording to claim 44 further comprising a liquid biomass tank fordiverting liquid biomass to the at least one biogas producing fermentor.51. The plant according to claim 44 further comprising a decantercentrifuge for separating fermented organic material into a semi-solidfraction comprising 30-40% (w/w) dry matter of which 2 to 10% (w/w) isphosphor, and a liquid fraction comprising reject water, furthercomprising means for diverting said liquid fraction obtained from saiddecanter centrifuge to said stripper device.
 52. The plant according toclaim 51, wherein the pre-filter separates particles larger than 0.1 μm(microns) from the reject water.
 53. The plant according to claim 51,wherein the pre-filter separates particles larger than 0.01 μm (microns)from the reject water.
 54. The plant according to claim 51, wherein thepre-filter separates particles larger than 0.001 μm (microns) from thereject water.
 55. The plant according to claim 51, wherein the permeateis used for flushing manure canals of an animal housing system.
 56. Theplant according to claim 44, wherein the stripper tank is connected to abiogas producing multi-step fermentor system comprising three fermentorscapable of operating at both thermophile conditions and mesophileconditions, wherein each fermentor is connected to said system.
 57. Theplant according to claim 51 further comprising a reverse osmosis unitfor separating potassium from the liquid fraction comprising rejectwater from which ammonia has been stripped, wherein the reverse osmosisunit comprises a) a pre-filter, and b) a reverse osmosis filter forfiltering a permeate resulting from ceramic filtration.
 58. The systemaccording to claim 1, further including means for diverting said aqueousliquid medium stripped for at least part of said volatile compounds backto one of the at least one fermentor and/or at least one biogas reactorfrom which the liquid medium was originally obtained.
 59. The systemaccording to claim 1, said system further comprising a phase separatorand means for diverting said condensate comprising volatile compoundsand vapor not condensed by the second condensing device from said secondcondensing device to a phase separator for separating said condensatecomprising volatile compounds and vapor not condensed by the secondcondensing device.
 60. A method for controlling the fermentation oforganic material comprising undesirable volatile compounds, said methodcomprising the steps of a) providing a fermentor comprising a liquidmedium comprising organic material and a biomass capable of fermentingsaid organic material, b) diverting said liquid medium to a side streamof the fermentor in the form of a shunt, c) contacting said liquidmedium in said shunt with cold steam at a first pressure below 1 bar,thereby obtaining a cold steam comprising volatile compounds and liquidmedium at least partly stripped for volatile compounds, d) condensingsaid cold steam comprising volatile compounds, thereby obtaining a firstcondensed liquid medium, e) injecting hot steam into said firstcondensed liquid medium at a second pressure of at least 1 bar, f)stripping off at least part of said volatile compounds comprised in saidfirst condensed liquid medium, and obtaining a hot steam of volatilecompounds and a condensed liquid medium stripped for essentially allvolatile compounds, and g) redirecting said liquid medium at leastpartly stripped for volatile compounds in step c) to said fermentor,and/or returning said condensed liquid medium stripped for essentiallyall volatile compounds in step f) to said shunt or to said fermentor,wherein said stripping of volatile compounds and said redirection ofsaid at least partly stripped liquid medium controls the fermentation ofsaid organic material.
 61. The method of claim 60 wherein said volatilecompounds include ammonia and said liquid medium of step a) is rejectwater.
 62. A method for stripping volatile compounds from a liquidmedium, said method comprising the steps of a) providing an aqueousliquid medium comprising volatile compounds, and b) diverting saidliquid medium comprising volatile compounds to a shunt operably linkedto a heating source and a condensing device, c) obtaining cold steam inan evaporator by adding heat to a sample of aqueous liquid and reducingthe pressure below a predetermined reference pressure, and d) directingsaid cold steam through said liquid medium comprising volatile compoundsin the shunt of the stripper device at said pressure below thepredetermined reference pressure, thereby stripping off volatilecompounds and obtaining a cold volatile compound-comprising steam, ande) diverting said cold volatile compound-comprising steam at saidpressure below the predetermined reference pressure to a firstcondensing device, and f) condensing in a first condensing step saidcold volatile compound-comprising steam at said pressure below thepredetermined reference pressure, thereby obtaining a first condensedaqueous liquid medium comprising volatile compounds, and g) divertingsaid first condensed aqueous liquid medium comprising volatile compoundto a stripper unit, and h) stripping off the volatile compound from saidfirst condensed aqueous liquid medium comprising volatile compound byheating said first condensed aqueous liquid in said stripper unit at ahigher second pressure, and obtaining a liquid with a reducedconcentration of volatile compounds.
 63. The method according to claim62, where said predetermined reference pressure is 1 bar.
 64. The methodof claim 62, wherein the system according to claim 1 is used foroperating the method.
 65. The method of claim 62, wherein in step f) isfurther obtained a vapor not condensed by the first condensing device,and said vapor not condensed by the first condensing device is divertedto a further condensing device at said pressure below a predeterminedreference pressure, removing part of the remaining volatile compoundsfrom said vapor not condensed by the first condensing device by washingin a counter current of aqueous liquid, obtaining a aqueous liquidfraction comprising volatile compounds and vapor not condensed by thefurther condensing device.
 66. The method of claim 65, wherein in stepg) said aqueous liquid fraction comprising volatile compounds is furtherdiverted to said stripper unit, and wherein in step h) volatilecompounds are stripped from said first condensed aqueous liquid mediumcomprising volatile compounds and said aqueous liquid fractioncomprising volatile compounds by heating at said second pressure,thereby obtaining a hot volatile compounds-comprising steam and aqueousliquid stripped off at least part of said volatile compounds.
 67. Themethod of claim 66, wherein said hot volatile compound-comprising steamis diverted to a second condensing device, condensing said hot volatilecompound-comprising steam at or above said reference pressure, therebyobtaining a second condensed aqueous liquid medium comprising volatilecompounds and vapor not condensed by the second condensing device. 68.The method of claim 62, wherein the aqueous liquid medium stripped forat least part of said volatile compounds is returned to the fermentor orbiogas reactor from which the liquid medium was originally obtained. 69.The method of claim 68, wherein the aqueous liquid medium returned tothe fermentor or biogas reactor is stripped for at least 20% of itscontent of volatile compounds.
 70. The method of claim 62, wherein saidpredetermined reference pressure is 1 bar.
 71. The method of claim 70,wherein the first pressure is from about 0.1 to 0.42 bar.
 72. The methodof claim 70, wherein the second pressure is from about 1 to 4 bar. 73.The method of claim 62, wherein said volatile compound is selected fromthe group of ammonia and volatile amines.
 74. The method of claim 73,wherein said volatile compound is ammonia.
 75. The method of claim 62,wherein said pressure below a predetermined reference pressure isobtained in the evaporator, the shunt, the first condensing device and afurther condensing device.
 76. The method of claim 62, wherein saidpressure in the evaporator below a predetermined reference pressure isin the range of from 0.1 to 1.0 bar.
 77. The method of claim 76, whereinsaid pressure below a predetermined reference pressure in the firstcondensing device and in a further condensing device is about 0.2 bar.78. The method of claim 76, wherein the pressure in the stripper unit isabout 2.5 bar.
 79. The method of claim 62, wherein the cold steam isobtained by heating aqueous liquid in the evaporator to a temperature of50 to 80° C.
 80. The method of claim 62, wherein the temperature of saidfirst condensed aqueous liquid medium comprising volatile compoundsand/or vapor not condensed by the first condensing device is 15-35° C.81. The method of claim 62, wherein the temperature of a counter currentof aqueous liquid in a further condensing device is 15-35° C.
 82. Themethod of claim 62, wherein the temperature of said first condensedaqueous liquid medium comprising volatile compounds and/or of saidaqueous liquid fraction comprising volatile compounds in the stripperunit is 80-170° C.
 83. The method of claim 82, wherein the temperatureis from about 100° C. to about 150° C.
 84. The method of claim 62,wherein the temperature of a second condensed aqueous liquid and/orvapor not condensed by a second condensing device is 15-45° C.
 85. Themethod of claim 62, wherein said aqueous liquid medium comprisingvolatile compounds comprises an amount of from 2.5 to 85 kg volatilecompounds per m3 (cubic meter).
 86. The method of claim 62, wherein theliquid medium comprising volatile compounds is liquid medium comprisingorganic materials.
 87. The method of claim 62, wherein the cold volatilecompounds-comprising steam comprises volatile compounds in aconcentration of about 0.53 to 109% volatile compounds.
 88. The methodof claim 62, wherein said aqueous liquid medium comprising a reducedconcentration of volatile compounds is directed to a bioreactor.
 89. Themethod of claim 62, wherein biomasses selected from the group consistingof meat and bone meal, vegetable protein, molasses, vinasse, andcombinations thereof are fermented.
 90. The method of claim 89, whereinthe amount of meat and bone meal fermented in a bioreactor comprisesmore than 2.5% of the total biomass by weight.
 91. The method of claim88, wherein the bioreactor is a mesophilic or thermophilic bioreactor.92. The method of claim 62, wherein the heating process in theevaporator is conducted by using heat exchangers reusing heat frommachines, engines or motor generators, or by adding to the evaporatorwarm waste aqueous liquids, or aqueous liquid obtained from acooling/condensing device.
 93. The method of claim 62, wherein thevolatile compound is ammonia, and wherein said condensed aqueous,ammonia comprising liquid resulting from condensation in said secondcondensing device is of commercial fertiliser grade.
 94. The method ofclaim 62, wherein said vapor not condensed by the second and/or secondcondensing device is directed to an air scrubber or directly to theatmosphere.